Voice: per-room voice flag — make a room VC or text-only

[hardlygospel]

What

Voice is currently a single server-wide channel with no per-room control. This adds the control plane to make a room VC or text-only:

• room-voice #room on / room-voice #room off in the /mod console.
• view #room now shows the room's voice: on/off flag.

How

• Schema: new chat_rooms.voice_enabled column (migration 074), defaults to false so every existing room stays text-only until a moderator opts it in. Model gains the field and a ChatRoom::set_voice_enabled setter.
• Command: folded into the moderation module exactly like rename-room — new RoomVoice { slug, enabled } command, a new SET_ROOM_VOICE capability granted to moderators, an audit-log entry, and help text (help room-voice).

Scope / follow-up

This is the per-room control + data layer — the part that makes "a room is VC or not" a real, mod-managed property. Giving each enabled room its own separate call (room-keyed LiveKit rooms instead of the one shared channel) is a deliberate follow-up: voice presence and join/listen tickets are currently keyed to one fixed room over the native CLI websocket and the browser listener HTTP endpoint, so true per-room calls need matching changes on both clients. I kept this PR server-side and migration-light so the flag can land and be built on.

Tests

• Command parser: room-voice #x on/off parse correctly and reject missing/invalid state.
• Existing chat/room-search suites updated for the new model field and stay green.

cargo build + the moderation/chat/room-search suites pass; no new clippy warnings.

Thanks 🙏

• mat (@mpiorowski) — for late.sh, and for the voice + moderation foundations this extends. The room model and mod-command framework made this a small, clean addition. Thank you.