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 `///`).

date_planner/lib/event_row.dart

@@ -31,9 +31,9 @@ class EventRow extends StatelessWidget {
             event.isComplete
                 ? const Icon(CupertinoIcons.check_mark)
                 : Text(
-                  '${event.remainingTaskCount}',
-                  style: const TextStyle(color: CupertinoColors.systemGrey),
-                ),
+                    '${event.remainingTaskCount}',
+                    style: const TextStyle(color: CupertinoColors.systemGrey),
+                  ),
             const CupertinoListTileChevron(),
           ],
         ),