ci: add GitHub Actions workflow + dev docs + test:all script

- .github/workflows/ci.yml: runs shared + server tests on push/PR
- docs/DEVELOPMENT.md: setup, run, test, architecture, status
- package.json: test:all script (shared + server suites)

.github/workflows/ci.yml

@@ -0,0 +1,22 @@
+name: CI
+
+on:
+  push:
+    branches: [main, rework-backend]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+          cache: 'npm'
+      - run: npm ci
+      - name: shared tests
+        run: npm test --workspace shared
+      - name: server tests
+        run: npm test --workspace server