Remove CI workflow (no Forgejo runner; quality gate runs locally via make check)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -1,25 +0,0 @@
-name: CI
-
-on:
-  push:
-    branches: [main, master]
-  pull_request:
-
-jobs:
-  test:
-    name: Analyze & test
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-
-      - uses: subosito/flutter-action@v2
-        with:
-          flutter-version: 3.44.0
-          channel: stable
-          cache: true
-
-      - name: Install dependencies
-        run: flutter pub get
-
-      - name: Run quality gate
-        run: make check