f39ff8c215
Add browser abstraction layer (compat.ts) that normalizes Chrome/Firefox/ Edge/Safari extension APIs behind a unified promise-based interface. Replace all direct chrome.* calls with compat layer across service worker, sync engine, badge, storage, popup, and options modules. - Browser-specific manifests in manifests/ (Firefox MV3 with gecko settings, Edge/Safari variants) - Multi-target build system: `npm run build` produces all four browser builds in build/<browser>/ - Per-browser build scripts: build:chrome, build:firefox, build:edge, build:safari - Auto-detects browser at runtime for platform-specific device registration - All 38 existing tests pass, typecheck clean Co-Authored-By: Paperclip <noreply@paperclip.ing>