ci: port analyze/test gate to Forgejo Actions, retire .gitlab-ci.yml

git.comunes.org is Forgejo. Replicates the analyze + commons_core/app_seeds test
gate in .forgejo/workflows/ci.yml (per-push + PR). Dropped the GitLab-only Windows
job (no Forgejo Windows runner).

.forgejo/workflows/ci.yml

@@ -0,0 +1,51 @@
+# Per-push gate for git.comunes.org (Forgejo Actions): analyze + tests.
+# Mirrors the local verification gate in docs/design/testing.md. Ported from the
+# retired .gitlab-ci.yml. Flutter pinned to the developer toolchain (3.41.9).
+#
+# NOTE: `runs-on` must match a label your Forgejo runner registered with; adjust
+# if the Comunes runner uses something other than `docker`.
+
+name: ci
+
+on:
+  push:
+    branches: ['**']
+  pull_request:
+
+jobs:
+  analyze:
+    runs-on: docker
+    container:
+      image: ghcr.io/cirruslabs/flutter:3.41.9
+    steps:
+      - uses: actions/checkout@v4
+      - run: flutter pub get
+      - run: dart format --output=none --set-exit-if-changed .
+      - run: flutter analyze
+
+  test-commons-core:
+    runs-on: docker
+    container:
+      image: ghcr.io/cirruslabs/flutter:3.41.9
+    steps:
+      - uses: actions/checkout@v4
+      - run: flutter pub get
+      - name: dart test
+        working-directory: packages/commons_core
+        run: dart test
+
+  test-app-seeds:
+    runs-on: docker
+    container:
+      image: ghcr.io/cirruslabs/flutter:3.41.9
+    steps:
+      - uses: actions/checkout@v4
+      # SQLCipher so the "no plaintext at rest" security test actually runs.
+      - run: apt-get update -qq && apt-get install -y -qq libsqlcipher-dev
+      - run: flutter pub get
+      - name: Generate code + test
+        working-directory: apps/app_seeds
+        run: |
+          dart run slang
+          dart run build_runner build --delete-conflicting-outputs
+          flutter test --coverage