Adds an inline preview for stored document files alongside download.
- API Server: GET /api/documents/{id}/file honours ?inline=1, serving an
inline Content-Disposition so the browser renders the file instead of
forcing a download (default stays attachment).
- Web App: BFF forwards the inline flag; documentPreviewUrl() helper; an eye
icon; and a preview modal (Teleported to body) that picks a viewer from the
file extension — images -> <img>, PDFs/text -> <iframe>, else a
download-instead fallback. Closes on backdrop click or Escape.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
