feat(external-llm): add native gemini CLI models

Added gemini CLI models:
- gemini/gemini-3-pro (long-context, reasoning)
- gemini/gemini-3-flash (fast, general)
- gemini/gemini-2.5-pro (long-context, reasoning)
- gemini/gemini-2.5-flash (fast, general)

Updated long-context routing to use native gemini CLI (gemini-3-pro)
instead of opencode/github-copilot path.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

state/model-policy.json

@@ -156,6 +156,30 @@
       "cli_args": ["-m", "opencode/big-pickle"],
       "use_cases": ["general"],
       "tier": "sonnet-equivalent"
+    },
+    "gemini/gemini-3-pro": {
+      "cli": "gemini",
+      "cli_args": ["-m", "gemini-3-pro"],
+      "use_cases": ["long-context", "reasoning"],
+      "tier": "opus-equivalent"
+    },
+    "gemini/gemini-3-flash": {
+      "cli": "gemini",
+      "cli_args": ["-m", "gemini-3-flash"],
+      "use_cases": ["fast", "general"],
+      "tier": "sonnet-equivalent"
+    },
+    "gemini/gemini-2.5-pro": {
+      "cli": "gemini",
+      "cli_args": ["-m", "gemini-2.5-pro"],
+      "use_cases": ["long-context", "reasoning"],
+      "tier": "opus-equivalent"
+    },
+    "gemini/gemini-2.5-flash": {
+      "cli": "gemini",
+      "cli_args": ["-m", "gemini-2.5-flash"],
+      "use_cases": ["fast", "general"],
+      "tier": "sonnet-equivalent"
     }
   },
   "claude_to_external_map": {
@@ -166,7 +190,7 @@
   "task_routing": {
     "reasoning": "github-copilot/gpt-5.2",
     "code-generation": "zai-coding-plan/glm-4.7",
-    "long-context": "github-copilot/gemini-3-pro-preview",
+    "long-context": "gemini/gemini-3-pro",
     "default": "github-copilot/claude-sonnet-4.5"
   }
 }