Step 1.4: add Gitea Actions CI workflow

Runs install, type-check, lint and test on every push and pull request.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -0,0 +1,19 @@
+name: CI
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+      - uses: pnpm/action-setup@v6
+      - uses: actions/setup-node@v7
+        with:
+          node-version-file: .nvmrc
+      - run: pnpm install --frozen-lockfile
+      - run: pnpm typecheck
+      - run: pnpm lint
+      - run: pnpm test