Real-browser tests (Playwright) and housekeeping

- npm run test:e2e builds the app, runs it on port 3101 with an empty throwaway
  database and drives Chrome (the installed one; no browser download) through
  notes and the paste check, the daily five minutes and weekly recall,
  translation compare (Bible text faked), and two-screen presenting.
- Vitest skips e2e/; ESLint knows the e2e folder and playwright.config.js.
- .gitignore: the local demo video, Playwright output and sign-in file.
- README and TODO describe the browser tests and what CI still needs.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

e2e/start-server.sh

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+# Builds the app and runs the server on port 3101 with a fresh, empty data folder (so tests never touch real studies).
+set -euo pipefail
+cd "$(dirname "$0")/.."
+export DATA_DIR="$(mktemp -d)"
+export PORT=3101
+export NODE_ENV=production
+npx vite build --logLevel error
+exec node server/index.js