fix(gemini): list Gemini 3 preview models in google-gemini-cli/gemini pickers (#12776)

The google-gemini-cli (Cloud Code Assist) and gemini (native API) model
pickers only offered gemini-2.5-*, so users picking Gemini 3 had to type
a custom model name — usually wrong (e.g. "gemini-3.1-pro"), producing
a 404 from cloudcode-pa.googleapis.com.

Replace the 2.5-* entries with the actual Code Assist / Gemini API
preview IDs: gemini-3.1-pro-preview, gemini-3-pro-preview,
gemini-3-flash-preview (and gemini-3.1-flash-lite-preview on native).
Update the hardcoded fallback in hermes_cli/main.py to match.

Copilot's menu retains gemini-2.5-pro — that catalog is Microsoft's.

hermes_cli/models.py

@@ -128,16 +128,14 @@ _PROVIDER_MODELS: dict[str, list[str]] = {
     ],
     "gemini": [
         "gemini-3.1-pro-preview",
+        "gemini-3-pro-preview",
         "gemini-3-flash-preview",
         "gemini-3.1-flash-lite-preview",
-        "gemini-2.5-pro",
-        "gemini-2.5-flash",
-        "gemini-2.5-flash-lite",
     ],
     "google-gemini-cli": [
-        "gemini-2.5-pro",
-        "gemini-2.5-flash",
-        "gemini-2.5-flash-lite",
+        "gemini-3.1-pro-preview",
+        "gemini-3-pro-preview",
+        "gemini-3-flash-preview",
     ],
     "zai": [
         "glm-5.1",