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 `///`).

compass_app/app/pubspec.yaml

@@ -3,9 +3,10 @@ description: >-
   A sample app that helps users build and book itineraries for trips.
 publish_to: none
 version: 0.1.0
+resolution: workspace
 
 environment:
-  sdk: ^3.7.0-0
+  sdk: ^3.9.0-0
 
 dependencies:
   cached_network_image: ^3.4.1
@@ -15,7 +16,7 @@ dependencies:
     sdk: flutter
   flutter_svg: ^2.0.16
   freezed_annotation: ^2.4.4
-  go_router: ^14.6.2
+  go_router: ^16.0.0
   google_fonts: ^6.2.1
   intl: any
   json_annotation: ^4.9.0
@@ -25,15 +26,16 @@ dependencies:
   shared_preferences: ^2.3.5
 
 dev_dependencies:
+  analysis_defaults:
+    path: ../../analysis_defaults
   flutter_test:
     sdk: flutter
-  flutter_lints: ^5.0.0
   mocktail_image_network: ^1.2.0
   mocktail: ^1.0.4
   integration_test:
     sdk: flutter
   build_runner: ^2.4.14
-  freezed: ^2.5.7
+  freezed: ^3.0.0
   json_serializable: ^6.9.0
 
 flutter: