Dart 3.9 / Flutter 3.35 [first LLM release] (#2714)

I got carried away with Gemini and basically rewrote CI and the release
process for the new LLM reality. This work was largely completed by
Gemini.

- Bump all SDK versions to the current beta (3.9.0-0)
- Run `flutter channel beta`
- Wrote `ci_script.dart` to replace the bash scripts
- Converted repository to pub workspace #2499 
- Added llm.md and release.md
- Added redirect for deprecated Samples Index

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I have added sample code updates to the [changelog].
- [x] I updated/added relevant documentation (doc comments with `///`).

form_app/lib/src/http/mock_client.dart

@@ -11,7 +11,8 @@ Future<http.Response> _mockHandler(http.Request request) async {
     json.decode(request.body) as Map<String, dynamic>,
   );
 
-  if (decodedJson['email'] == 'root' && decodedJson['password'] == 'password') {
+  if (decodedJson['email'] == 'root' &&
+      decodedJson['password'] == 'password') {
     return http.Response('', 200);
   }