build: add a browser-test exclusion check and a pre-push static-check hook

npm run check:browser-excludes finds tests that import a browser driver and
asks `vitest list` whether the CI config still collects them; wired into CI.
npm install now also installs a marker-owned pre-push hook that runs the
static CI checks (~15s). Skip with CODEMAN_SKIP_PREPUSH=1; hand-written
hooks are left alone.

.github/CONTRIBUTING.md

@@ -28,12 +28,15 @@ The frontend is plain JS served from `src/web/public/` with no bundler in dev: e
 CI runs all of these, so save yourself a round trip:
 
 ```bash
-npm run typecheck              # tsc --noEmit, strict mode
+npm run typecheck               # tsc --noEmit, strict mode
 npm run lint
 npm run format:check
-npm run check:frontend-syntax  # syntax-checks the plain-JS frontend modules
+npm run check:frontend-syntax   # syntax-checks the plain-JS frontend modules
+npm run check:browser-excludes  # every browser-driven test is kept out of `npm test`
 ```
 
+`npm install` also installs a `pre-push` git hook that runs these static checks (~15s) and blocks the push if one fails. Skip it once with `CODEMAN_SKIP_PREPUSH=1 git push`; it never replaces a `pre-push` hook of your own.
+
 ### Tests
 
 ```bash

.github/workflows/ci.yml

@@ -34,6 +34,13 @@ jobs:
       - name: Frontend JS syntax check
         run: npm run check:frontend-syntax
 
+      # Asks `vitest list` what CI would actually collect, rather than matching
+      # filenames: a browser-driven test missing from BROWSER_TEST_GLOBS
+      # (config/test-suites.ts) passes locally and dies in the test job with
+      # "browserType.launch: Executable doesn't exist".
+      - name: Browser-test exclusion check
+        run: npm run check:browser-excludes
+
       - name: Format check
         run: npm run format:check