v0.12.2

Patch release fixing three bugs found during v0.12.1 testing — all in the config CLI / `SIGHUP` reload surface.

## Fixed
- **`siphon-ai check` silently swallowed config load-time warnings** (security-relevant). The read-only subcommands installed no tracing subscriber, so compile-time warnings — notably the **SRTP-master-key-in-cleartext** footgun (a gateway with `srtp != off` but a non-TLS transport) — were dropped, making the documented preflight *less* informative than a real boot. `check` now surfaces exactly what the daemon prints at startup (then still reports `config OK` + exit 0 — these are warnings, not errors). **Re-run `siphon-ai check` on your configs after upgrading** — it may surface warnings the preflight was previously hiding.
- **SIGHUP webhook/CDR-spool reload warning over-fired.** With a `spool_dir` configured, every reload logged "delivery changes require a restart" even when `[webhooks]`/`[cdr]` hadn't changed. It now fires only on a real change (and the reload no longer needlessly rebuilds an unchanged sink).
- **`[media]` restart-required check missed codec / DTMF changes** (silent config drift). Changing `[media].codecs` (or any `[bridge]` default) and reloading was silently swallowed — not hot-applied, no warning. The restart-required fingerprint now covers the full `[media]` block + the bridge/codec defaults.

No config or protocol changes; drop-in upgrade from 0.12.x.

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