feat(mobile): add opt-in terminal controls

[Lint111]

Summary

Add one opt-in mobile terminal control system with responsive surfaces for keyboard-open and keyboard-hidden states.

Controls

• Keyboard hidden:
  • Esc at the left edge
  • Up, Enter, and Down centered
  • Tab at the right edge
  • vertical swipe on the surrounding band sends Up or Down
  • pressing Up and Down together sends one Enter without leaking arrow keys
• Keyboard open:
  • compact accessory row with Esc, arrows, Option+Enter, Tab/Shift+Tab, paste, path insertion, clear input, CLI commands, and dismiss
  • fixed-height horizontal layout keeps primary actions inside narrow phone widths
• Optional feedback:
  • short vibration when navigator.vibrate is available
  • short Web Audio tone when enabled

Interaction Safety

• Pointer gestures claim the interaction before button activation, so a swipe that begins or ends on a button does not also click it.
• Canceled pointers clear pressed state without dispatch.
• Controls hide while Codeman dialogs are open and return afterward.
• Terminal-control taps do not focus xterm or open the mobile keyboard.
• Active web views suppress terminal controls.
• Existing upstream path-picker and clear-input accessory actions are preserved.

Settings and Migration

• Mobile Terminal Controls, haptics, and sound are available in App Settings on touch devices.
• Controls and haptics default off.
• Explicit canonical or legacy true preferences migrate to enabled.
• Legacy extendedKeyboardBar: false and device detection alone do not enable the new controls.

Volume Keys

Codeman maps browser keydown events reported as volume up/down and applies the same simultaneous-direction Enter chord. This is progressive enhancement only: most mobile browsers reserve physical volume keys at the operating-system level and do not expose those events to web pages. The visible controls are the reliable interface.

Validation

• npx vitest run --config config/vitest.config.ts test/mobile-navigation-pad.test.ts
  • 21 tests passed
• npx vitest run --config test/mobile/vitest.config.ts test/mobile/navigation-pad.test.ts
  • 10 Playwright-backed tests passed
• npx vitest run --config test/mobile/vitest.config.ts test/mobile/settings.test.ts
  • 20 Playwright-backed tests passed
• npx vitest run --config test/mobile/vitest.config.ts test/mobile/keyboard.test.ts -t "control rows|unified terminal-control|unified controls|accessory bar"
  • 4 focused tests passed
• npm run check:frontend-syntax
  • 26 frontend files passed
• npm run build
  • passed

Scope

This PR does not change terminal tap classification, draft/IME/paste handling, PTY viewport ownership, or terminal-history streaming. Those are separate review slices.