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 `///`).

date_planner/lib/task_row.dart

@@ -29,14 +29,13 @@ class _TaskRowState extends State<TaskRow> {
     return Row(
       children: [
         CupertinoButton(
-          onPressed:
-              widget.isEditing
-                  ? () {
-                    setState(() {
-                      widget.task.isCompleted = !widget.task.isCompleted;
-                    });
-                  }
-                  : null,
+          onPressed: widget.isEditing
+              ? () {
+                  setState(() {
+                    widget.task.isCompleted = !widget.task.isCompleted;
+                  });
+                }
+              : null,
           child: Icon(
             widget.task.isCompleted
                 ? CupertinoIcons.checkmark_circle_fill
@@ -45,15 +44,14 @@ class _TaskRowState extends State<TaskRow> {
           ),
         ),
         Expanded(
-          child:
-              widget.isEditing
-                  ? CupertinoTextField(
-                    decoration: null,
-                    padding: EdgeInsets.zero,
-                    controller: _taskText,
-                    onChanged: (value) => widget.task.text = value,
-                  )
-                  : Text(widget.task.text),
+          child: widget.isEditing
+              ? CupertinoTextField(
+                  decoration: null,
+                  padding: EdgeInsets.zero,
+                  controller: _taskText,
+                  onChanged: (value) => widget.task.text = value,
+                )
+              : Text(widget.task.text),
         ),
       ],
     );