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 `///`).

navigation_and_routing/lib/src/screens/scaffold.dart

@@ -31,8 +31,14 @@ class BookstoreScaffold extends StatelessWidget {
         },
         destinations: const [
           AdaptiveScaffoldDestination(title: 'Books', icon: Icons.book),
-          AdaptiveScaffoldDestination(title: 'Authors', icon: Icons.person),
-          AdaptiveScaffoldDestination(title: 'Settings', icon: Icons.settings),
+          AdaptiveScaffoldDestination(
+            title: 'Authors',
+            icon: Icons.person,
+          ),
+          AdaptiveScaffoldDestination(
+            title: 'Settings',
+            icon: Icons.settings,
+          ),
         ],
       ),
     );