Add copilot-setup-steps.yml to install Flutter/Dart in agent environment

Co-authored-by: jaredmixpanel <10504508+jaredmixpanel@users.noreply.github.com>

Author: Copilot

.github/copilot-instructions.md

@@ -35,10 +35,10 @@ tool/                           # Build scripts (bump_version.sh)
 
 ## Essential Commands
 
-**Flutter and Dart are not installed in the sandbox environment.** You cannot run `flutter test`, `dart analyze`, or `dart format` directly. Rely on CI for validation.
+Flutter and Dart are pre-installed by `.github/workflows/copilot-setup-steps.yml`. You can run all standard commands directly.
 
 ```bash
-# Unit tests (requires Flutter SDK)
+# Unit tests
 flutter test
 
 # Unit tests excluding golden tests (for compat-check on older Flutter)

.github/workflows/copilot-setup-steps.yml

@@ -0,0 +1,37 @@
+name: "Copilot Setup Steps"
+
+on:
+  workflow_dispatch:
+  push:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+  pull_request:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+
+jobs:
+  copilot-setup-steps:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up Flutter
+        uses: subosito/flutter-action@fd55f4c5af5b953cc57a2be44cb082c8f6635e8e # v2.21.0
+        with:
+          channel: stable
+          flutter-version: "3.41.2"
+          cache: true
+
+      - name: Install dependencies
+        run: flutter pub get
+
+      - name: Verify setup
+        run: |
+          echo "Flutter version:"
+          flutter --version
+          echo ""
+          echo "Dart version:"
+          dart --version