ci: run typecheck, build & tests on PRs and main (#6)

* ci: run typecheck, build & tests on PRs and main

Add a GitHub Actions workflow (.github/workflows/ci.yml) that installs on
Node 20 (the pinned runtime), builds shared/server/web, typechecks desktop,
and runs the full vitest suite across all packages on every pull request and
push to main. The repo already had 500+ tests but only ever ran them locally.

Also wires up the missing test/typecheck plumbing this exposed:
- web package had 55 test files but no test script — add test/test:watch/typecheck
- add root-level test and typecheck aggregate scripts
- fix a latent web type error the new typecheck surfaced: reference
  vite-plugin-pwa/react types so virtual:pwa-register/react is typed
  (useRegisterSW callback params were implicit any; the tsc half of the web
  build script has been failing, masked by vite build ignoring type errors)

* test: fix two latent failures surfaced by CI on Node 20

- server: exclude dist/** from vitest. Vitest 4's default exclude dropped
  dist/, so after `pnpm build` emits compiled .test.js files, vitest ran those
  stale copies alongside src/*.test.ts and they failed (compiled vi.mock paths
  resolve differently).
- web: polyfill Blob.prototype.stream in the jsdom test setup. jsdom's Blob has
  no .stream() on Node 20 (Node 25 provided one, masking this locally); undici's
  Response constructor calls blob.stream(), so new Response(blob) threw
  'object.stream is not a function'.

packages/server/vitest.config.ts

@@ -1,7 +1,13 @@
-import { defineConfig } from 'vitest/config';
+import { defineConfig, configDefaults } from 'vitest/config';
 
 export default defineConfig({
   test: {
     setupFiles: ['./test/setup-env.ts'],
+    // Vitest 4's default `exclude` is only node_modules/.git — it no longer
+    // ignores dist/. Once `pnpm build` (tsc) has emitted the compiled test files
+    // into dist/, vitest would otherwise run those stale .js copies alongside the
+    // real src/*.test.ts — and they fail, because compiled vi.mock() paths
+    // resolve differently than the source. Never run build output as tests.
+    exclude: [...configDefaults.exclude, 'dist/**'],
   },
 });