Scaffold V3.1 directory structure and document implementation plan

[Copilot]

V3_1Plan.md specifies a workflow upgrade: Clip Library, Look Mixer, and Look Controller modes on top of the existing live designer, reduced to 2 outputs.

Completed

• V3_1/sender/: Directory scaffolded for new implementation
• Full V3.0 codebase analysis: All effects, Art-Net transport, HTTP server, embedded UI, state persistence mapped

Not yet implemented

The core deliverable V3_1/sender/led_controller.py was not created — the session ran out of time. The detailed architecture is documented in the PR description checklist for the next session to pick up:

• 2-output config: Remove A2, keep A0/A1
• Clip system: clips.json persistence, naming convention (OpeningScene_sStrip1, OpeningScene_grid1), CRUD API (/api/clips, /api/clips/save|delete|load)
• Look system: looks.json persistence, timeline tracks with beat positions, CRUD + playback API (/api/looks, /api/looks/save|delete|trigger|stop)
• 4-tab UI: Clip Designer (existing editor + save), Clip Library (card grid, search/sort), Look Mixer (beat-grid timeline), Look Controller (theatre-style trigger buttons)
• Preserve: All Art-Net compliance, effects engine, device management, FPS telemetry