v1.10.0 - G.722 + Opus codec support for conference and voicemail

Built and deployed on commit 705e231 (production IMAGE_TAG=git-705e2314,
healthy, 2h+ uptime). Includes all post-merge fixes:
- Dockerfile: libopus0 added to runtime image (build had it but runtime was missing)
- Migration 012_voicemail_sample_rate.sql renamed to 021_voicemail_sample_rate.sql
  (collided with v1.9.2's 012_voicemail.sql)

Release v1.9.2 - fix nginx heredoc on legacy builder (frontend 502)

Release v1.9.1 - Post-v1.9.0 fixes (CI base image + REST API startup …

…panic)

v1.9.0 - Tier 1 batch (Prometheus, OpenAPI, config reload, webhooks, …

…voicemail email, CDR export)

Release v1.8.0: conference PIN, TURN health, CDR auto-archive, API ra…

…te limiting, voicemail PIN

v1.7.0: busy-to-voicemail + voicemail IVR navigation

Release v1.6.0: Phase 1 code quality improvements

- Refactored handler.rs into message.rs and response.rs
- Extracted magic numbers into CleanupConfig
- Added thiserror custom error types
- Added 36 new tests (189 lib + 65 integration + 26 frontend)

Release v1.3.0