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/src/providers/google-gemini-cli.ts

@@ -953,7 +953,10 @@ export function buildRequest(
 	}
 
 	if (context.tools && context.tools.length > 0) {
-		request.tools = convertTools(context.tools);
+		// Claude models on Cloud Code Assist need the legacy `parameters` field;
+		// the API translates it into Anthropic's `input_schema`.
+		const useParameters = model.id.startsWith("claude-");
+		request.tools = convertTools(context.tools, useParameters);
 		if (options.toolChoice) {
 			request.toolConfig = {
 				functionCallingConfig: {