[WIP] Merge PR #4 and apply necessary fixes

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Original prompt

Pull request: #20

Step 1. Merge PR #4 first. Apply Copilot's db.waitForPendingWrites() fix manually before merging so the localStorage backup isn't cleared before Firebase confirms receipt. Apply the history.go(1) popstate fix. Add user-select: text to the PID display element in the CSS.
Step 2. From PR #18, cherry-pick only three things: the crypto.randomUUID() change (add a safe fallback for non-HTTPS edge cases), removal of all console calls, and the textContent fix. Do not take the broken catch block from #18 — PR #4's version is better.
Step 3. Merge PR #5 after applying Gemini's fade-out fix (delay display:none on outgoing screen by 400ms to match CSS transition duration).
Step 4. Merge PRs #7, #9, #13, #17 — these are clean, non-conflicting.
Step 5. Check if PR #6 is now redundant given PR #4's localStorage implementation. If the logic is identical, close #6. If it adds something, merge it.
Step 6. Fix the Playwright tests in PRs #8, #11, #12, #14, #15, #16 before merging any of them — replace all asyncio.sleep() with expect() assertions, fix the unawaited coroutine in the route handler, add domcontentloaded wait.
Step 7. Add benchmark.html to Firebase Hosting ignore rules in firebase.json.
Step 8. Replace [Your Name / Email] in the README

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