chore: add GitHub community files and CI pipeline

- .github/workflows/ci.yml: TypeScript check + Vitest + build on every PR
- .github/dependabot.yml: weekly npm + Actions updates (minor/patch grouped)
- .github/ISSUE_TEMPLATE/: bug_report, feature_request, config (→ Discussions)
- .github/PULL_REQUEST_TEMPLATE.md: checklist for contributors
- SECURITY.md: responsible disclosure policy via GitHub Advisories
- CONTRIBUTING.md: dev setup, code style, commit conventions

.github/workflows/ci.yml

@@ -0,0 +1,43 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+# Cancel in-progress runs for the same PR / branch
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  ci:
+    name: Type-check & Test
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: TypeScript – type check
+        run: npx tsc --noEmit
+
+      - name: Run tests
+        run: npx vitest run
+
+      - name: Build
+        run: npm run build
+        env:
+          # Minimal env vars so Next.js build doesn't bail early on env validation
+          IMMICH_URL: http://localhost:2283
+          IMMICH_API_KEY: placeholder-key-for-ci