v0.12.0 — Shared state across browsers, a results view, and your name in the header

The web app's selection and format choices now live on the server, so every
browser, tab, and device pointed at the app shows the same ticked books, the
same formats, and the same live progress. The header shows your account
email/name instead of a generic "Signed in", and a new results view makes a
failed download easy to find among hundreds of successes.

Added

• Server-side shared UI state. Which books are selected and your preferred
  ebook/audiobook formats now live on the backend (GET / POST /prefs, and
  folded into the /activity poll every browser already makes) instead of each
  browser's localStorage/sessionStorage. Open the app in a second browser
  mid-download and it shows the same selection and progress. Persisted to
  LITRES_STATE_FILE (defaults onto the Docker /data volume), so it also
  survives a restart.
• Account identity in the header. A cookie-only session (e.g. in Docker,
  where there's no OS keychain to remember the login name) now recovers your
  email/login from litres.ru's /users/me, so the header shows who you are
  rather than a generic "Signed in".
• Results view with a status filter. After a build, a summary shows
  All N · ✓ done · ! skipped · ✗ failed as clickable pills -- one click
  filters the log to just the failures, so a single rights-limited title no
  longer hides among hundreds of successes.
• End-to-end / smoke tests. An offline e2e suite (real server boot + full
  login → build → download flow + the MCP tool flow) plus an opt-in
  pytest -m live suite that smoke-tests a running instance.

Fixed

• The results and the download link survive a page reload. The cache-only
  size-check that runs on every page load used to wipe the finished build's
  per-book results and its zip download link. Both are now kept until the
  next build starts, so you can reload to inspect failures and still download
  the zip.
• A build where every selected title failed no longer offers an empty zip.

Changed

• New LITRES_STATE_FILE setting (default .litres_state.json; /data/...
  in Docker) holds the shared UI state; it's git-ignored like the session and
  cache files.