fix(ai): use parametersJsonSchema for Google tool declarations, revert Antigravity opus model

- Use parametersJsonSchema instead of parameters for Gemini tool declarations
  to support full JSON Schema (anyOf, oneOf, const, etc.)
- Keep legacy parameters field for Claude models on Cloud Code Assist, where
  the API translates parameters into Anthropic's input_schema
- Revert claude-opus-4-6-thinking back to claude-opus-4-5-thinking (model
  doesn't exist on the Antigravity endpoint)

fixes #1398

packages/ai/scripts/generate-models.ts

@@ -1021,8 +1021,8 @@ async function generateModels() {
 			maxTokens: 64000,
 		},
 		{
-			id: "claude-opus-4-6-thinking",
-			name: "Claude Opus 4.6 Thinking (Antigravity)",
+			id: "claude-opus-4-5-thinking",
+			name: "Claude Opus 4.5 Thinking (Antigravity)",
 			api: "google-gemini-cli",
 			provider: "google-antigravity",
 			baseUrl: ANTIGRAVITY_ENDPOINT,