dsh-browser-install: auto-install Playwright Chromium and bridge it for dsh-ego-browser

On load, ensures the Playwright browser target (default: chromium) is installed
via `npx --yes playwright install chromium --with-deps` (background when missing,
so profile startup is not blocked), then symlinks the installed binary at
/usr/local/bin/google-chrome-stable (+ chromium). That exact name is what
dsh-ego-browser's PATH scan and its bundled --no-sandbox wrapper both look for,
so root/Docker containers get a working agent browser with zero manual PATH,
env-var or wrapper steps. Pre-existing user binaries/wrappers are never
clobbered. Ships as a dsh bundle (plain ESM, no build step); install via
`dsh plugin --profile web add github:<you>/dsh-browser-install#main` and update
with `dsh plugin --profile web update` (branch ref resolves the tip).

.gitignore

@@ -0,0 +1,4 @@
+node_modules/
+pnpm-lock.yaml
+*.log
+.DS_Store