ci: lint, typecheck, test and build both images

Works on GitHub and Gitea/Forgejo Actions. Not run yet: no remote or
runner configured.

Task: M0-T7

.github/workflows/ci.yml

@@ -0,0 +1,28 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+# Runs on GitHub Actions and Gitea/Forgejo Actions (both read .github/workflows).
+name: ci
+on:
+  push:
+  pull_request:
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: pnpm/action-setup@v4 # version comes from package.json "packageManager"
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 24
+          cache: pnpm
+      - run: pnpm install --frozen-lockfile
+      - run: pnpm lint
+      - run: pnpm typecheck
+      - run: pnpm test
+
+  images:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - run: docker build -f apps/api/Dockerfile -t selfphoneng-api:ci .
+      - run: docker build -t selfphoneng-asterisk:ci asterisk