fix(antigravity): update user-agent and fix schema validation

Update hardcoded User-Agent to 1.15.8 in @mariozechner/pi-ai via pnpm patch to resolve "version not supported" error.
Add sanitizeToolUseInput helper to ensure tool_use payloads include the required input field.
Update src/infra usage fetcher User-Agent to match supported version.
Fix unit test pi-embedded-runner.google-sanitize-thinking.test.ts to expect input field in tool calls.

src/agents/pi-embedded-runner.google-sanitize-thinking.test.ts

@@ -224,12 +224,14 @@ describe("sanitizeSessionHistory (google thinking)", () => {
       {
         type: "toolCall",
         id: "call_1",
+        input: {},
         name: "read",
         arguments: { path: "/tmp/foo" },
       },
       {
         type: "toolCall",
         id: "call_2",
+        input: {},
         name: "read",
         arguments: { path: "/tmp/bar" },
         thoughtSignature: "c2ln",