feat(nous): free-tier model gating, pricing display, and vision fallback

- Show pricing during initial Nous Portal login (was missing from
  _login_nous, only shown in the already-logged-in hermes model path)

- Filter free models for paid subscribers: non-allowlisted free models
  are hidden; allowlisted models (xiaomi/mimo-v2-pro, xiaomi/mimo-v2-omni)
  only appear when actually priced as free

- Detect free-tier accounts via portal api/oauth/account endpoint
  (monthly_charge == 0); free-tier users see only free models as
  selectable, with paid models shown dimmed and unselectable

- Use xiaomi/mimo-v2-omni as the auxiliary vision model for free-tier
  Nous users so vision_analyze and browser_vision work without paid
  model access (replaces the default google/gemini-3-flash-preview)

- Unavailable models rendered via print() before TerminalMenu to avoid
  simple_term_menu line-width padding artifacts; upgrade URL resolved
  from auth state portal_base_url (supports staging/custom portals)

- Add 21 tests covering filter_nous_free_models, is_nous_free_tier,
  and partition_nous_models_by_tier

tests/hermes_cli/test_models.py

@@ -1,6 +1,10 @@
 """Tests for the hermes_cli models module."""
 
-from hermes_cli.models import OPENROUTER_MODELS, menu_labels, model_ids, detect_provider_for_model
+from hermes_cli.models import (
+    OPENROUTER_MODELS, menu_labels, model_ids, detect_provider_for_model,
+    filter_nous_free_models, _NOUS_ALLOWED_FREE_MODELS,
+    is_nous_free_tier, partition_nous_models_by_tier,
+)
 
 
 class TestModelIds:
@@ -124,3 +128,166 @@ class TestDetectProviderForModel:
         result = detect_provider_for_model("claude-opus-4-6", "openai-codex")
         assert result is not None
         assert result[0] not in ("nous",)  # nous has claude models but shouldn't be suggested
+
+
+class TestFilterNousFreeModels:
+    """Tests for filter_nous_free_models — Nous Portal free-model policy."""
+
+    _PAID = {"prompt": "0.000003", "completion": "0.000015"}
+    _FREE = {"prompt": "0", "completion": "0"}
+
+    def test_paid_models_kept(self):
+        """Regular paid models pass through unchanged."""
+        models = ["anthropic/claude-opus-4.6", "openai/gpt-5.4"]
+        pricing = {m: self._PAID for m in models}
+        assert filter_nous_free_models(models, pricing) == models
+
+    def test_free_non_allowlist_models_removed(self):
+        """Free models NOT in the allowlist are filtered out."""
+        models = ["anthropic/claude-opus-4.6", "arcee-ai/trinity-large-preview:free"]
+        pricing = {
+            "anthropic/claude-opus-4.6": self._PAID,
+            "arcee-ai/trinity-large-preview:free": self._FREE,
+        }
+        result = filter_nous_free_models(models, pricing)
+        assert result == ["anthropic/claude-opus-4.6"]
+
+    def test_allowlist_model_kept_when_free(self):
+        """Allowlist models are kept when they report as free."""
+        models = ["anthropic/claude-opus-4.6", "xiaomi/mimo-v2-pro"]
+        pricing = {
+            "anthropic/claude-opus-4.6": self._PAID,
+            "xiaomi/mimo-v2-pro": self._FREE,
+        }
+        result = filter_nous_free_models(models, pricing)
+        assert result == ["anthropic/claude-opus-4.6", "xiaomi/mimo-v2-pro"]
+
+    def test_allowlist_model_removed_when_paid(self):
+        """Allowlist models are removed when they are NOT free."""
+        models = ["anthropic/claude-opus-4.6", "xiaomi/mimo-v2-pro"]
+        pricing = {
+            "anthropic/claude-opus-4.6": self._PAID,
+            "xiaomi/mimo-v2-pro": self._PAID,
+        }
+        result = filter_nous_free_models(models, pricing)
+        assert result == ["anthropic/claude-opus-4.6"]
+
+    def test_no_pricing_returns_all(self):
+        """When pricing data is unavailable, all models pass through."""
+        models = ["anthropic/claude-opus-4.6", "nvidia/nemotron-3-super-120b-a12b:free"]
+        assert filter_nous_free_models(models, {}) == models
+
+    def test_model_with_no_pricing_entry_treated_as_paid(self):
+        """A model missing from the pricing dict is kept (assumed paid)."""
+        models = ["anthropic/claude-opus-4.6", "openai/gpt-5.4"]
+        pricing = {"anthropic/claude-opus-4.6": self._PAID}  # gpt-5.4 not in pricing
+        result = filter_nous_free_models(models, pricing)
+        assert result == models
+
+    def test_mixed_scenario(self):
+        """End-to-end: mix of paid, free-allowed, free-disallowed, allowlist-not-free."""
+        models = [
+            "anthropic/claude-opus-4.6",       # paid, not allowlist → keep
+            "nvidia/nemotron-3-super-120b-a12b:free",  # free, not allowlist → drop
+            "xiaomi/mimo-v2-pro",              # free, allowlist → keep
+            "xiaomi/mimo-v2-omni",             # paid, allowlist → drop
+            "openai/gpt-5.4",                  # paid, not allowlist → keep
+        ]
+        pricing = {
+            "anthropic/claude-opus-4.6": self._PAID,
+            "nvidia/nemotron-3-super-120b-a12b:free": self._FREE,
+            "xiaomi/mimo-v2-pro": self._FREE,
+            "xiaomi/mimo-v2-omni": self._PAID,
+            "openai/gpt-5.4": self._PAID,
+        }
+        result = filter_nous_free_models(models, pricing)
+        assert result == [
+            "anthropic/claude-opus-4.6",
+            "xiaomi/mimo-v2-pro",
+            "openai/gpt-5.4",
+        ]
+
+    def test_allowlist_contains_expected_models(self):
+        """Sanity: the allowlist has the models we expect."""
+        assert "xiaomi/mimo-v2-pro" in _NOUS_ALLOWED_FREE_MODELS
+        assert "xiaomi/mimo-v2-omni" in _NOUS_ALLOWED_FREE_MODELS
+
+
+class TestIsNousFreeTier:
+    """Tests for is_nous_free_tier — account tier detection."""
+
+    def test_paid_plus_tier(self):
+        assert is_nous_free_tier({"subscription": {"plan": "Plus", "tier": 2, "monthly_charge": 20}}) is False
+
+    def test_free_tier_by_charge(self):
+        assert is_nous_free_tier({"subscription": {"plan": "Free", "tier": 0, "monthly_charge": 0}}) is True
+
+    def test_no_charge_field_not_free(self):
+        """Missing monthly_charge defaults to not-free (don't block users)."""
+        assert is_nous_free_tier({"subscription": {"plan": "Free", "tier": 0}}) is False
+
+    def test_plan_name_alone_not_free(self):
+        """Plan name alone is not enough — monthly_charge is required."""
+        assert is_nous_free_tier({"subscription": {"plan": "free"}}) is False
+
+    def test_empty_subscription_not_free(self):
+        """Empty subscription dict defaults to not-free (don't block users)."""
+        assert is_nous_free_tier({"subscription": {}}) is False
+
+    def test_no_subscription_not_free(self):
+        """Missing subscription key returns False."""
+        assert is_nous_free_tier({}) is False
+
+    def test_empty_response_not_free(self):
+        """Completely empty response defaults to not-free."""
+        assert is_nous_free_tier({}) is False
+
+
+class TestPartitionNousModelsByTier:
+    """Tests for partition_nous_models_by_tier — free vs paid tier model split."""
+
+    _PAID = {"prompt": "0.000003", "completion": "0.000015"}
+    _FREE = {"prompt": "0", "completion": "0"}
+
+    def test_paid_tier_all_selectable(self):
+        """Paid users get all models as selectable, none unavailable."""
+        models = ["anthropic/claude-opus-4.6", "xiaomi/mimo-v2-pro"]
+        pricing = {"anthropic/claude-opus-4.6": self._PAID, "xiaomi/mimo-v2-pro": self._FREE}
+        sel, unav = partition_nous_models_by_tier(models, pricing, free_tier=False)
+        assert sel == models
+        assert unav == []
+
+    def test_free_tier_splits_correctly(self):
+        """Free users see only free models; paid ones are unavailable."""
+        models = ["anthropic/claude-opus-4.6", "xiaomi/mimo-v2-pro", "openai/gpt-5.4"]
+        pricing = {
+            "anthropic/claude-opus-4.6": self._PAID,
+            "xiaomi/mimo-v2-pro": self._FREE,
+            "openai/gpt-5.4": self._PAID,
+        }
+        sel, unav = partition_nous_models_by_tier(models, pricing, free_tier=True)
+        assert sel == ["xiaomi/mimo-v2-pro"]
+        assert unav == ["anthropic/claude-opus-4.6", "openai/gpt-5.4"]
+
+    def test_no_pricing_returns_all(self):
+        """Without pricing data, all models are selectable."""
+        models = ["anthropic/claude-opus-4.6", "openai/gpt-5.4"]
+        sel, unav = partition_nous_models_by_tier(models, {}, free_tier=True)
+        assert sel == models
+        assert unav == []
+
+    def test_all_free_models(self):
+        """When all models are free, free-tier users can select all."""
+        models = ["xiaomi/mimo-v2-pro", "xiaomi/mimo-v2-omni"]
+        pricing = {m: self._FREE for m in models}
+        sel, unav = partition_nous_models_by_tier(models, pricing, free_tier=True)
+        assert sel == models
+        assert unav == []
+
+    def test_all_paid_models(self):
+        """When all models are paid, free-tier users have none selectable."""
+        models = ["anthropic/claude-opus-4.6", "openai/gpt-5.4"]
+        pricing = {m: self._PAID for m in models}
+        sel, unav = partition_nous_models_by_tier(models, pricing, free_tier=True)
+        assert sel == []
+        assert unav == models