Operator-only dependency subset (requests, rich, websockets, cryptography>=41,
srp) so the C-heavy cryptography>=46 server pin can be satisfied by Termux's
packaged build. Server requirements.txt is left unchanged. srp is best-effort:
the client falls back to the pure-Python shim when it can't be built.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>