630a0de970
The shared-key mode uses HKDF with empty info, but Element Call JS uses
participant identity as HKDF info. Per-participant mode (set_key with
identity) matches EC's derivation.
Previous per-participant attempt (b65d043) failed because key rotation
(index 0→1 when bot joins) wasn't handled. Now on_encryption_key calls
set_key(caller_id, key, index) on rotation, so the bot stays in sync.
Changes:
- _build_e2ee_options(): remove caller_key param, shared_key=b"" (per-participant mode)
- _run(): set_key(remote_identity, caller_key, 0) for incoming decryption
- on_encryption_key: only set_key() on rotation (no set_shared_key)