ci: run typecheck + unit tests on push/PR

build.yml only built the APK — the 65 unit tests and typecheck never ran in CI,
so regressions in the covered logic (headers/SSE/diagnostics/settings/etc.) could
land silently. Add a fast 'test' job (Node 24, native TS test-running) so every
push and PR enforces typecheck + npm test before merge.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/build.yml

@@ -8,6 +8,27 @@ on:
     branches: [main]
 
 jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+
+      - uses: actions/setup-node@v6
+        with:
+          # Node >= 23.6 runs the TypeScript test files natively (type-stripping),
+          # matching the local toolchain. No build step or extra deps required.
+          node-version: 24
+          cache: npm
+
+      - name: Install dependencies
+        run: npm install --legacy-peer-deps
+
+      - name: Typecheck
+        run: npm run typecheck
+
+      - name: Unit tests
+        run: npm test
+
   build:
     runs-on: ubuntu-latest
     env: