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 `///`).

desktop_photo_search/material/pubspec.yaml

@@ -1,10 +1,11 @@
-name: desktop_photo_search
+name: desktop_photo_search_material
 description: Search for Photos, using the Unsplash API.
 publish_to: 'none'
 version: 1.0.0+1
+resolution: workspace
 
 environment:
-  sdk: ^3.7.0-0
+  sdk: ^3.9.0-0
 
 dependencies:
   built_collection: ^5.1.1
@@ -20,7 +21,6 @@ dependencies:
     git:
       url: https://github.com/google/flutter-desktop-embedding.git
       path: plugins/menubar
-      ref: 6c66ad23ee79749f30a8eece542cf54eaf157ed8
   provider: ^6.0.5
   transparent_image: ^2.0.1
   url_launcher: ^6.1.12
@@ -29,7 +29,6 @@ dependencies:
     git:
       url: https://github.com/google/flutter-desktop-embedding.git
       path: plugins/window_size
-      ref: 6c66ad23ee79749f30a8eece542cf54eaf157ed8
 
 dev_dependencies:
   analysis_defaults: