#4105 @swamp/video/obs: optional OBS recording with per-person hardware config for @swamp/video

Summary

@swamp/video/obs (private, optional, depends on @swamp/video, #4103): drive OBS over obs-websocket v5 so recording flows into video-edit. Ported and generalized from Adam's @adam/obs (git.swamp-club.com/swamp-club/swamp-video, extensions/behaviors/obs.ts, workflow-obs-setup.yaml, workflow-record-tutorial.yaml).

Hardware differs per person, so all of it lives in a per-user studio behavior instance, never in code defaults:

• detect: list webcams by stable /dev/v4l/by-id paths, audio inputs, available OBS input kinds (pipewire vs xcomposite screen capture) and usable encoders (vaapi, qsv, nvenc, x264), and propose a studio config. The prototype hard-codes Intel Quick Sync, 4K and a Razer webcam at /dev/video32; Seth's setup is 1440p, x264, a C920 and a Scarlett 2i2 with RNNoise/compressor/limiter.
• Two modes: managed (Adam's: configure canvas/recording/mic-only track and build the scene, optionally using the brand stage) and adopt (use an existing scene/profile as-is, only status/start/stop/markers). Seth's existing "Product Demo" profile must work under adopt unchanged.
• Markers: record a timestamp during recording (e.g. a retake marker) as data the core edit behavior consumes.
• record workflow: check idle, (managed: pick capture), start, suspend on a stop signal (keep with title / discard), stop, run video-edit.
• Websocket password from a vault.

Note from the prototype: after changing recording settings OBS must be restarted before its recording output picks them up; surface that clearly.