feat(brand): add the Traverse Board project icon

[Qiyuanqiii]

Summary

• adopt the maintainer-provided compass and route illustration as the official Traverse Board project icon
• use the same approved mark in the app shell, READMEs, browser favicon and touch icon, Windows EXE/MSIX packages, and the macOS app bundle
• document the source checksum and usage rules while replacing the temporary letter-based avatar

Asset handling

• preserve the supplied PNG exactly as the repository master (SHA-256 fb1260a41b49d7959dc731f4455d2022e55008bef9f73be6cbd674b08fa59a14)
• create platform derivatives only through deterministic resizing and container conversion; no generative redraw was used

Compatibility

• package identifiers, command names, configuration directories, environment variables, and schema identifiers remain unchanged

Validation

• npm test (66 files, 289 tests)
• npm run typecheck
• npm run build
• npm run check:api
• go test -tags "desktop,wv2runtime.error" -count=1 ./cmd/cyberagent-desktop ./internal/desktop ./internal/webui
• Windows amd64 and arm64 resource builds plus unsigned MSIX packaging
• macOS bundle-script syntax and ICNS resource validation
• Playwright visual QA on desktop/mobile and light/dark surfaces, with no browser console errors