fix: update Gemini model catalog + wire models.dev as live model source

Follow-up for salvaged PR #5494:
- Update model catalog to Gemini 3.x + Gemma 4 (drop deprecated 2.0)
- Add list_agentic_models() to models_dev.py with noise filter
- Wire models.dev into _model_flow_api_key_provider as primary source
  (static curated list serves as offline fallback)
- Add gemini -> google mapping in PROVIDER_TO_MODELS_DEV
- Fix Gemma 4 context lengths to 256K (models.dev values)
- Update auxiliary model to gemini-3-flash-preview
- Expand tests: 3.x catalog, context lengths, models.dev integration

hermes_cli/models.py

@@ -112,15 +112,15 @@ _PROVIDER_MODELS: dict[str, list[str]] = {
         "grok-code-fast-1",
     ],
     "gemini": [
+        "gemini-3.1-pro-preview",
+        "gemini-3-flash-preview",
+        "gemini-3.1-flash-lite-preview",
         "gemini-2.5-pro",
         "gemini-2.5-flash",
-        "gemini-2.0-flash",
-        "gemini-2.0-flash-lite",
+        "gemini-2.5-flash-lite",
         # Gemma open models (also served via AI Studio)
         "gemma-4-31b-it",
-        "gemma-4-26b-a4b-it",
-        "gemma-4-e4b-it",
-        "gemma-4-e2b-it",
+        "gemma-4-26b-it",
     ],
     "zai": [
         "glm-5",