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 `///`).

provider_shopper/lib/screens/catalog.dart

@@ -48,17 +48,16 @@ class _AddButton extends StatelessWidget {
     );
 
     return TextButton(
-      onPressed:
-          isInCart
-              ? null
-              : () {
-                // If the item is not in cart, we let the user add it.
-                // We are using context.read() here because the callback
-                // is executed whenever the user taps the button. In other
-                // words, it is executed outside the build method.
-                var cart = context.read<CartModel>();
-                cart.add(item);
-              },
+      onPressed: isInCart
+          ? null
+          : () {
+              // If the item is not in cart, we let the user add it.
+              // We are using context.read() here because the callback
+              // is executed whenever the user taps the button. In other
+              // words, it is executed outside the build method.
+              var cart = context.read<CartModel>();
+              cart.add(item);
+            },
       style: ButtonStyle(
         overlayColor: WidgetStateProperty.resolveWith<Color?>((states) {
           if (states.contains(WidgetState.pressed)) {
@@ -67,10 +66,9 @@ class _AddButton extends StatelessWidget {
           return null; // Defer to the widget's default.
         }),
       ),
-      child:
-          isInCart
-              ? const Icon(Icons.check, semanticLabel: 'ADDED')
-              : const Text('ADD'),
+      child: isInCart
+          ? const Icon(Icons.check, semanticLabel: 'ADDED')
+          : const Text('ADD'),
     );
   }
 }
@@ -79,7 +77,10 @@ class _MyAppBar extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return SliverAppBar(
-      title: Text('Catalog', style: Theme.of(context).textTheme.displayLarge),
+      title: Text(
+        'Catalog',
+        style: Theme.of(context).textTheme.displayLarge,
+      ),
       floating: true,
       actions: [
         IconButton(
@@ -111,7 +112,10 @@ class _MyListItem extends StatelessWidget {
         maxHeight: 48,
         child: Row(
           children: [
-            AspectRatio(aspectRatio: 1, child: Container(color: item.color)),
+            AspectRatio(
+              aspectRatio: 1,
+              child: Container(color: item.color),
+            ),
             const SizedBox(width: 24),
             Expanded(child: Text(item.name, style: textTheme)),
             const SizedBox(width: 24),