fix(ai): correct Google thinking detection and remove unsupported id fields

- isThinkingPart now only checks thought === true, not thoughtSignature
- thoughtSignature is for context replay and can appear on any part type
- Store thoughtSignature on text blocks as textSignature for proper replay
- Remove id from functionCall/functionResponse (unsupported by Vertex/Cloud Code Assist)

Refs: https://ai.google.dev/gemini-api/docs/thought-signatures
Co-authored-by: Amp <amp@ampcode.com>

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

@@ -511,6 +511,12 @@ export const streamGoogleGeminiCli: StreamFunction<"google-gemini-cli"> = (
 										});
 									} else {
 										currentBlock.text += part.text;
+										if (part.thoughtSignature) {
+											currentBlock.textSignature = retainThoughtSignature(
+												currentBlock.textSignature,
+												part.thoughtSignature,
+											);
+										}
 										stream.push({
 											type: "text_delta",
 											contentIndex: blockIndex(),