feat(keyboard): add configurable key repeat

[ZacharyZcR]

Summary

• add long-press repeat for navigation and editing keys
• expose bounded repeat delay and interval settings
• preserve repeat defaults when loading older keyboard configurations
• send the initial key immediately and stop timers cleanly on release or unmount
• retain the larger input focus surface from the original contribution

This rebases and resolves #36 onto dev-1.5.0. The original feature commits remain authored by Marcio Rinaldi (mrinaldi).

Verification

• npx tsc --noEmit
• npm run lint (0 errors; existing warnings only)
• npm run format:check
• git diff --check

Supersedes #36.