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.
