Vale construir sua versão de Tallymeter?

Build me a freelance time tracker that produces invoices, like Tallymeter. Requirements:

- Node + Express + better-sqlite3, one process, server-rendered pages on
  localhost:4820. No accounts, no telemetry, everything stays on my machine.
- Tables: clients, projects (hourly rate, currency), entries, invoices.
- One timer, big start/stop button on the index page: starting a new one stops
  the running one first, so two can never run at once. Entries store
  description, project, started_at and ended_at as ISO-8601 UTC.
- Let me edit a finished entry's description in place, and add one after the
  fact with a duration in minutes for the call I forgot to track. Entries
  already on an invoice are frozen, reject the edit.
- An /unbilled page: finished entries with no invoice_id, grouped by project,
  hours shown as "3h 25m" and the money at the project rate.
- Invoice a project's unbilled entries: one line per description with decimal
  hours, sequential INV-2026-001 numbers that are never reused even if I delete
  a draft, bank details and VAT rate from config.json, rendered to
  ./invoices/INV-2026-001.pdf with puppeteer. Stamp invoice_id on what it billed.
- Out of scope: multi-user accounts, payment collection, mobile apps. Skip them.
- README: config.json fields, where the PDFs land, and a warning that the
  sqlite file is the only copy of my billing history · tell me to back it up.