Sync wiki with docs/ at 5946a6d
docs: sync — Phase 3 progress and measured performance
docs: sync — Phase 2 complete, magnet association and tray platform notes
docs: sync — Phase 1 features (settings, file selection, drag-drop, clipboard)
docs: sync — Phase 0 recorded as merged
docs: sync — backend test layers, Phase 0 counts
docs: publish Flume wiki (architecture, engine notes, platform, CI, roadmap)