Route MLX load, inference, unload, reset, cache cleanup, and shutdown through a single worker. Add affinity and concurrent-unload regression coverage.\n\nVerified: 17 related backend tests; frontend CI; cargo check.
Move 9 business-logic modules from the backend root into services/: channels, effects, history, profiles, stories, versions, export_import, transcribe, tts. Move platform_detect.py into utils/. Backend root now contains only infrastructure (app, main, config, server, models, build_binary) and docs. All 94 routes verified.
Jamie Pine