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 `///`).

dynamic_theme/lib/widgets/api_key_widget.dart

@@ -44,11 +44,10 @@ class ApiKeyWidget extends StatelessWidget {
               Link(
                 uri: Uri.https('aistudio.google.com', '/app/apikey'),
                 target: LinkTarget.blank,
-                builder:
-                    (context, followLink) => TextButton(
-                      onPressed: followLink,
-                      child: const Text('Get an API Key'),
-                    ),
+                builder: (context, followLink) => TextButton(
+                  onPressed: followLink,
+                  child: const Text('Get an API Key'),
+                ),
               ),
             ],
           ),