Make OBS startup and connection more robust

[Broyojo]

What

Hardens the OBS integration against the most common failure modes, especially on macOS:

• Websocket connection retry with readiness probe — OBSClient previously called obs.ReqClient() once and crashed if OBS was still starting up (which it usually is, since DuckTrack launches it). Now retries up to 5 times, verifying with get_version().
• macOS launch via open -a OBS — launching the binary directly bypasses the normal app launch path, which breaks Screen Recording permission prompts. Correspondingly, close_obs now quits OBS via AppleScript on macOS (terminating the open process did nothing) with a killall fallback.
• Profile fallback — if the computer_tracker profile can't be created or switched to, continue with the current profile and warn, instead of crashing. Profile restore on stop is now guarded the same way.
• One-time macOS permissions notice — explains the Screen Recording / Accessibility / Input Monitoring requirements on first launch (relevant to Sluggish Movement on MacOS Sometimes #8 and DuckTrack does NOT opening in OSX - M1 Mac Ventura 13.6.6 #10, where recordings silently come out empty without them).

Notes

Builds on #12 (its commit is included here) — merge that first.

Credit

Adapted from the huyouare/DuckTrack fork by @huyouare, which debugged these failure modes on modern macOS. This PR takes the connection/launch/profile robustness ideas from that fork, reimplemented to match the existing code style (the fork's fallback input monitor and logging overhaul are intentionally not included, since the sentinel events it injects would break the events.jsonl schema that downstream consumers rely on).

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