feat(models): add Gemini 3.5 Flash models to registry

- Registered new models: `gemini-3-flash-agent` and `gemini-3.5-flash-low` with detailed specifications.
- Includes support for dynamic thinking levels and extended context capabilities.

internal/registry/models/models.json

@@ -1954,6 +1954,28 @@
         ]
       }
     },
+    {
+      "id": "gemini-3-flash-agent",
+      "object": "model",
+      "owned_by": "antigravity",
+      "type": "antigravity",
+      "display_name": "Gemini 3.5 Flash",
+      "name": "gemini-3-flash-agent",
+      "description": "Gemini 3.5 Flash",
+      "context_length": 1048576,
+      "max_completion_tokens": 65536,
+      "thinking": {
+        "min": 128,
+        "max": 32768,
+        "dynamic_allowed": true,
+        "levels": [
+          "minimal",
+          "low",
+          "medium",
+          "high"
+        ]
+      }
+    },
     {
       "id": "gemini-3-pro-high",
       "object": "model",
@@ -2087,7 +2109,29 @@
           "high"
         ]
       }
+    },
+    {
+      "id": "gemini-3.5-flash-low",
+      "object": "model",
+      "owned_by": "antigravity",
+      "type": "antigravity",
+      "display_name": "Gemini 3.5 Flash (Low)",
+      "name": "gemini-3.5-flash-low",
+      "description": "Gemini 3.5 Flash (Low)",
+      "context_length": 1048576,
+      "max_completion_tokens": 65535,
+      "thinking": {
+        "min": 1,
+        "max": 65535,
+        "dynamic_allowed": true,
+        "levels": [
+          "low",
+          "medium",
+          "high"
+        ]
+      }
     }
+
   ],
   "xai": [
     {