feat(06-03): create Gitea Actions multi-stage CI/CD pipeline

- Three chained jobs: quality (lint+type-check) -> test (vitest) -> build-deploy
- Uses plain docker compose build/up (not build-push-action, avoids Pitfall 4)
- Triggers on push to main branch only (D-11, D-12)
- No hardcoded secrets in workflow (T-06-08)

.gitea/workflows/ci.yml

@@ -0,0 +1,65 @@
+name: Tessera CI/CD
+
+on:
+  push:
+    branches: [main]
+
+jobs:
+  quality:
+    name: Lint & Type Check
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: pnpm/action-setup@v4
+        with:
+          version: 9
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 24
+          cache: pnpm
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Lint
+        run: pnpm lint
+
+      - name: Type check
+        run: pnpm type-check
+
+  test:
+    name: Tests
+    runs-on: ubuntu-latest
+    needs: quality
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: pnpm/action-setup@v4
+        with:
+          version: 9
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 24
+          cache: pnpm
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Run tests
+        run: pnpm test
+
+  build-deploy:
+    name: Build & Deploy
+    runs-on: ubuntu-latest
+    needs: test
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Build Docker images
+        run: docker compose build web api
+
+      - name: Deploy services
+        run: docker compose up -d web api