feat: Phase 0+1 — TypeScript + Biome infrastructure, src/common/ TS migration

- Add biome.json (replaces ESLint), tsconfig.json hierarchy (root/main/muya/renderer)
- Delete .eslintignore, .eslintrc.js
- Migrate src/common/ entirely to TypeScript:
  - commands/constants.js → .ts
  - encoding.js → .ts
  - envPaths.js → .ts
  - filesystem/index.js → .ts
  - filesystem/paths.js → .ts
  - keybinding/index.js → .ts
- Add src/common/electron.d.ts (Electron globals for renderer)
- Add src/common/types/preload.d.ts (window.api PreloadApi types)
- Add CLAUDE.md (architecture migration roadmap)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>