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/lib/ui/core/themes/dimens.dart

@@ -35,12 +35,11 @@ abstract final class Dimens {
   static const Dimens mobile = _DimensMobile();
 
   /// Get dimensions definition based on screen size
-  factory Dimens.of(BuildContext context) => switch (MediaQuery.sizeOf(
-    context,
-  ).width) {
-    > 600 && < 840 => desktop,
-    _ => mobile,
-  };
+  factory Dimens.of(BuildContext context) =>
+      switch (MediaQuery.sizeOf(context).width) {
+        > 600 && < 840 => desktop,
+        _ => mobile,
+      };
 }
 
 /// Mobile dimensions

compass_app/app/lib/ui/core/ui/custom_checkbox.dart

@@ -28,10 +28,9 @@ class CustomCheckbox extends StatelessWidget {
         ),
         child: Material(
           borderRadius: BorderRadius.circular(24),
-          color:
-              value
-                  ? Theme.of(context).colorScheme.primary
-                  : Colors.transparent,
+          color: value
+              ? Theme.of(context).colorScheme.primary
+              : Colors.transparent,
           child: SizedBox(
             width: 24,
             height: 24,