v0.34.0

### Added

- **WS-failure prompt playback** — `[bridge].on_ws_failure =
  "play_prompt"` + `ws_failure_prompt_file`, both per-route
  overridable (`docs/design/DESIGN_WS_FAILURE_PROMPT.md`; #292).
  Finishes the switch reserved since v1: when the WS becomes
  **unusable** — unexpected drop, connect failure at answer, keepalive
  timeout, `protocol_error`, `server_too_slow`, or an exhausted
  0.7.3 reconnect window — the caller hears a configurable WAV
  (*"we're experiencing difficulties…"*) before the normal BYE,
  instead of an unexplained disconnect. Details:
  - Never fires when the ending was intended (server `hangup` / clean
    `stop`), on caller actions, on `rtp_timeout`, or during drain.
  - **Fail-open**: an unusable prompt (rate mismatch, file vanished)
    degrades to today's immediate teardown; playback is capped at a
    fixed 30 s. CDR termination causes are unchanged (`duration_ms`
    grows by the prompt).
  - **Announce-over-park**: a prompt started while the call is parked
    on MOH now plays (MOH → prompt → BYE after a failed reconnect);
    a park arriving mid-announcement still cuts it short, so the
    0.26.0 consent semantics are unchanged.
  - Prompt file is required + existence-checked at load when any
    effective policy is `play_prompt`; WAVs longer than the 30 s cap
    warn at load.
- **Metric**: `siphon_ai_ws_failure_prompts_total{result}` with
  `played | cut_short | unusable | timeout`.
- **SIPp harness**: `ws_failure_prompt` phase (echo server drops the
  WS mid-call; asserts the prompt played on a real call). Suite is
  now 38 scenarios.

### Changed

- `MediaTap::with_ws_reconnect` renamed to `with_survive_ws_drop`
  (internal API) — the tap's survive-WS-drop mode now serves both
  reconnect and prompt calls.

No WS-protocol, CDR, or webhook-schema changes.

---

**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:v0.34.0` (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
```