January hardening: SRTP, licensing plumbing, honest recordings

A platform-hardening month. SIP domains gained Secure Media support, so SRTP-encrypted calls work out of the box. The licensing infrastructure that powers the in-module purchase flow was ported in, marking the 2.0 line. Recordings now start when a call is answered instead of while it rings, so your archive stops collecting ringtones. The default call duration limit settled at a production-friendly 2 hours.