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

agent/auxiliary_client.py

@@ -91,6 +91,7 @@ auxiliary_is_nous: bool = False
 # Default auxiliary models per provider
 _OPENROUTER_MODEL = "google/gemini-3-flash-preview"
 _NOUS_MODEL = "google/gemini-3-flash-preview"
+_NOUS_FREE_TIER_VISION_MODEL = "xiaomi/mimo-v2-omni"
 _NOUS_DEFAULT_BASE_URL = "https://inference-api.nousresearch.com/v1"
 _ANTHROPIC_DEFAULT_BASE_URL = "https://api.anthropic.com"
 _AUTH_JSON_PATH = get_hermes_home() / "auth.json"
@@ -720,7 +721,19 @@ def _try_nous() -> Tuple[Optional[OpenAI], Optional[str]]:
     global auxiliary_is_nous
     auxiliary_is_nous = True
     logger.debug("Auxiliary client: Nous Portal")
-    model = "gemini-3-flash" if nous.get("source") == "pool" else _NOUS_MODEL
+    if nous.get("source") == "pool":
+        model = "gemini-3-flash"
+    else:
+        model = _NOUS_MODEL
+    # Free-tier users can't use paid auxiliary models — use the free
+    # multimodal model instead so vision/browser-vision still works.
+    try:
+        from hermes_cli.models import check_nous_free_tier
+        if check_nous_free_tier():
+            model = _NOUS_FREE_TIER_VISION_MODEL
+            logger.debug("Free-tier Nous account — using %s for auxiliary/vision", model)
+    except Exception:
+        pass
     return (
         OpenAI(
             api_key=_nous_api_key(nous),