Add Vercel fx as a first-class terminal agent

Orca supports arbitrary terminal agents, but Vercel fx is not available as a first-class selectable agent.

Requested scope:
- detect and launch the Vercel fx interactive CLI without confusing it with the unrelated `fx` JSON viewer
- support local, WSL, SSH, and folder workspaces
- map Orca Manual/Yolo modes to fx permission modes
- classify interactive and resumed sessions while excluding utility commands
- detect live permission dialogs before sending queued prompts
- add desktop/mobile catalog and documentation coverage

Known upstream limitation: fx 0.0.8 discards kitty keypad code points 57399–57427 even though Orca forwards those bytes unchanged, so Num Lock keypad handling requires an fx parser fix rather than an Orca terminal rewrite.