docs: Gemini OAuth provider implementation plan (#2467)

* docs: add Gemini OAuth provider implementation plan

Planning doc for a standard-route Gemini provider using Google OAuth
(Authorization Code + PKCE) with the OpenAI-compatible endpoint at
generativelanguage.googleapis.com. Covers OAuth flow, token lifecycle,
file list, and estimated scope (~700 lines).

Replaces the Node.js bridge approach from PR #2042.

* chore: update OpenRouter model list

- Add xiaomi/mimo-v2-pro
- Add nvidia/nemotron-3-super-120b-a12b (paid, higher rate limits)
- Remove openrouter/hunter-alpha and openrouter/healer-alpha (discontinued)

hermes_cli/models.py

@@ -31,8 +31,7 @@ OPENROUTER_MODELS: list[tuple[str, str]] = [
     ("anthropic/claude-haiku-4.5",      ""),
     ("openai/gpt-5.4",                  ""),
     ("openai/gpt-5.4-mini",             ""),
-    ("openrouter/hunter-alpha",          "free"),
-    ("openrouter/healer-alpha",          "free"),
+    ("xiaomi/mimo-v2-pro",               ""),
     ("openai/gpt-5.3-codex",            ""),
     ("google/gemini-3-pro-preview",     ""),
     ("google/gemini-3-flash-preview",   ""),
@@ -44,6 +43,7 @@ OPENROUTER_MODELS: list[tuple[str, str]] = [
     ("z-ai/glm-5-turbo",                ""),
     ("moonshotai/kimi-k2.5",            ""),
     ("x-ai/grok-4.20-beta",             ""),
+    ("nvidia/nemotron-3-super-120b-a12b",      ""),
     ("nvidia/nemotron-3-super-120b-a12b:free", "free"),
     ("arcee-ai/trinity-large-preview:free", "free"),
     ("openai/gpt-5.4-pro",              ""),