Track the frontend lockfile so npm ci can work

The ignore rule for package-lock.json had no leading slash, so it matched at
any depth and kept frontend/package-lock.json out of the repository. The
frontend CI job meanwhile installs with npm ci and caches against that exact
path, neither of which can work when the file is absent from a clean checkout.
The rule is now anchored to the repository root and the lockfile is tracked.

.gitignore

@@ -224,9 +224,15 @@ __marimo__/
 
 # custom ignores
 dist
-package-lock.json
+/package-lock.json
 yarn.lock
 
+# Playwright (frontend/e2e)
+frontend/e2e/.auth/
+frontend/playwright-report/
+frontend/test-results/
+frontend/blob-report/
+
 # Created by https://www.gitignore.io/api/node,macos
 
 ### macOS ###