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 `///`).

gemini_tasks/lib/widgets/message_widget.dart

@@ -30,17 +30,17 @@ class MessageWidget extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return Row(
-      mainAxisAlignment:
-          isFromUser ? MainAxisAlignment.end : MainAxisAlignment.start,
+      mainAxisAlignment: isFromUser
+          ? MainAxisAlignment.end
+          : MainAxisAlignment.start,
       children: [
         Flexible(
           child: Container(
             constraints: const BoxConstraints(maxWidth: 520),
             decoration: BoxDecoration(
-              color:
-                  isFromUser
-                      ? Theme.of(context).colorScheme.primaryContainer
-                      : Theme.of(context).colorScheme.surfaceContainerHighest,
+              color: isFromUser
+                  ? Theme.of(context).colorScheme.primaryContainer
+                  : Theme.of(context).colorScheme.surfaceContainerHighest,
               borderRadius: BorderRadius.circular(18),
             ),
             padding: const EdgeInsets.symmetric(vertical: 15, horizontal: 20),