v0.47.1

### Added

- **`offset_ms` extended to `dtmf`, `silence_detected`, and `dead_air_detected`** (completes issue #394 — 0.47.0 added it to the speech events). Same semantics and anchor: monotonic milliseconds between `start` being written to the socket and the event's trigger — the digit's *end* detection for `dtmf`, the detector poll that crossed the threshold for the idle pair (so the idle events' offset carries the same up-to-500 ms poll quantization their `duration_ms` already has). Stamped at detection, saturating to `0` for triggers that predate `start` on the wire. Additive within protocol v1; absent from older daemons; documented in PROTOCOL.md §3.4/§3.6/§3.7, typed in both server SDKs.

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**Artifacts**

- Static musl binaries for `x86_64` and `aarch64` (`.tar.gz`).
- Debian packages (`.deb`) for `amd64` and `arm64` — `apt install ./siphon-ai_*_amd64.deb`.
- `SHA256SUMS` — verify with `sha256sum -c SHA256SUMS`.
- `*-sbom.cdx.json` — CycloneDX SBOM.
- `SHA256SUMS.cosign.bundle` — cosign keyless signature over the checksums.
- Container: `ghcr.io/thevoiceguy/siphon-ai:v0.47.1` (multi-arch, cosign-signed).

Verify the checksums signature:
```
cosign verify-blob --bundle SHA256SUMS.cosign.bundle \
  --certificate-oidc-issuer https://token.actions.githubusercontent.com \
  --certificate-identity-regexp 'release.yml@' SHA256SUMS
```