feat: curated picker with live pricing for ai-gateway provider

- Curated AI_GATEWAY_MODELS list in hermes_cli/models.py (OSS first,
  kimi-k2.5 as recommended default).
- fetch_ai_gateway_models() filters the curated list against the live
  /v1/models catalog; falls back to the snapshot on network failure.
- fetch_ai_gateway_pricing() translates Vercel's input/output field
  names to the prompt/completion shape the shared picker expects;
  carries input_cache_read / input_cache_write through unchanged.
- get_pricing_for_provider() now handles ai-gateway.
- _model_flow_ai_gateway() provides a guided URL prompt when no key
  is set and a pricing-column picker; routes ai-gateway to it instead
  of the generic api-key flow.

tests/hermes_cli/test_ai_gateway_models.py

@@ -0,0 +1,129 @@
+"""AI Gateway model list and pricing translation.
+
+Vercel AI Gateway exposes ``/v1/models`` with a richer shape than OpenAI's
+spec (type, tags, pricing). The pricing object uses ``input`` / ``output``
+where hermes's shared picker expects ``prompt`` / ``completion``; these tests
+pin the translation and the curated-list filtering.
+"""
+import json
+from unittest.mock import patch, MagicMock
+
+from hermes_cli import models as models_module
+from hermes_cli.models import (
+    AI_GATEWAY_MODELS,
+    _ai_gateway_model_is_free,
+    fetch_ai_gateway_models,
+    fetch_ai_gateway_pricing,
+)
+
+
+def _mock_urlopen(payload):
+    """Build a urlopen() context manager mock returning the given payload."""
+    resp = MagicMock()
+    resp.read.return_value = json.dumps(payload).encode()
+    ctx = MagicMock()
+    ctx.__enter__.return_value = resp
+    ctx.__exit__.return_value = False
+    return ctx
+
+
+def _reset_caches():
+    models_module._ai_gateway_catalog_cache = None
+    models_module._pricing_cache.clear()
+
+
+def test_ai_gateway_pricing_translates_input_output_to_prompt_completion():
+    _reset_caches()
+    payload = {
+        "data": [
+            {
+                "id": "moonshotai/kimi-k2.5",
+                "type": "language",
+                "pricing": {
+                    "input": "0.0000006",
+                    "output": "0.0000025",
+                    "input_cache_read": "0.00000015",
+                    "input_cache_write": "0.0000006",
+                },
+            }
+        ]
+    }
+    with patch("urllib.request.urlopen", return_value=_mock_urlopen(payload)):
+        result = fetch_ai_gateway_pricing(force_refresh=True)
+
+    entry = result["moonshotai/kimi-k2.5"]
+    assert entry["prompt"] == "0.0000006"
+    assert entry["completion"] == "0.0000025"
+    assert entry["input_cache_read"] == "0.00000015"
+    assert entry["input_cache_write"] == "0.0000006"
+
+
+def test_ai_gateway_pricing_returns_empty_on_fetch_failure():
+    _reset_caches()
+    with patch("urllib.request.urlopen", side_effect=OSError("network down")):
+        result = fetch_ai_gateway_pricing(force_refresh=True)
+    assert result == {}
+
+
+def test_ai_gateway_pricing_skips_entries_without_pricing_dict():
+    _reset_caches()
+    payload = {
+        "data": [
+            {"id": "x/y", "pricing": None},
+            {"id": "a/b", "pricing": {"input": "0", "output": "0"}},
+        ]
+    }
+    with patch("urllib.request.urlopen", return_value=_mock_urlopen(payload)):
+        result = fetch_ai_gateway_pricing(force_refresh=True)
+    assert "x/y" not in result
+    assert result["a/b"] == {"prompt": "0", "completion": "0"}
+
+
+def test_ai_gateway_free_detector():
+    assert _ai_gateway_model_is_free({"input": "0", "output": "0"}) is True
+    assert _ai_gateway_model_is_free({"input": "0", "output": "0.01"}) is False
+    assert _ai_gateway_model_is_free({"input": "0.01", "output": "0"}) is False
+    assert _ai_gateway_model_is_free(None) is False
+    assert _ai_gateway_model_is_free({"input": "not a number"}) is False
+
+
+def test_fetch_ai_gateway_models_filters_against_live_catalog():
+    _reset_caches()
+    preferred = [mid for mid, _ in AI_GATEWAY_MODELS]
+    live_ids = preferred[:3]  # only first three exist live
+    payload = {
+        "data": [
+            {"id": mid, "pricing": {"input": "0.001", "output": "0.002"}}
+            for mid in live_ids
+        ]
+    }
+    with patch("urllib.request.urlopen", return_value=_mock_urlopen(payload)):
+        result = fetch_ai_gateway_models(force_refresh=True)
+
+    assert [mid for mid, _ in result] == live_ids
+    assert result[0][1] == "recommended"
+
+
+def test_fetch_ai_gateway_models_tags_free_models():
+    _reset_caches()
+    first_id = AI_GATEWAY_MODELS[0][0]
+    second_id = AI_GATEWAY_MODELS[1][0]
+    payload = {
+        "data": [
+            {"id": first_id, "pricing": {"input": "0.001", "output": "0.002"}},
+            {"id": second_id, "pricing": {"input": "0", "output": "0"}},
+        ]
+    }
+    with patch("urllib.request.urlopen", return_value=_mock_urlopen(payload)):
+        result = fetch_ai_gateway_models(force_refresh=True)
+
+    by_id = dict(result)
+    assert by_id[first_id] == "recommended"
+    assert by_id[second_id] == "free"
+
+
+def test_fetch_ai_gateway_models_falls_back_on_error():
+    _reset_caches()
+    with patch("urllib.request.urlopen", side_effect=OSError("network")):
+        result = fetch_ai_gateway_models(force_refresh=True)
+    assert result == list(AI_GATEWAY_MODELS)