Adds a second flow alongside the URL-to-EPUB pipeline:
- New POST /send-file endpoint accepts multipart/form-data with a `file`
and `readerEmail`, attaches the file to an email, and ships it to the
reader as-is. No conversion — the device decides what it accepts
(EPUB, PDF, MOBI, FB2, ...).
- 25 MB cap enforced both client-side and server-side (multer).
- Shares the same 20/hour rate limit as /send-article (now sendLimiter).
- UI: dropzone with drag/drop + click-to-pick + visible filename feedback.
- Shared e-reader email input across both flows.
- Codeberg source link added to the footer.
- Version bumped 0.1.0 → 0.2.0.
Prevents abuse before exposing the app publicly. Limits each client IP to
20 article sends per hour. trust proxy is set so the real client IP is
used (not Nginx's loopback) once the app is behind a reverse proxy.
