feat(loop): add Pause, Resume, Next Round, and Restart flow controls

Research Loop Panel now has a full state-aware control bar:

- IDLE: dropdown + 'Run Loop' (with confirm dialog as before)
- RUNNING: 'Pause' (soft stop preserving cycle count) + 'Stop' (hard stop)
- PAUSED: amber badge showing 'Paused at N/M cycles' + 'Resume'
  (restarts with remaining cycles) + 'Restart' (clean slate)
- DONE: 'Next Round' (immediate restart, no confirm) + 'Restart'
  (clear results and start fresh)

Status badge now shows Running/Paused/Done/Ready states with
appropriate colours. Cycle selector hidden while running or paused.
startLoop() accepts optional iterationOverride for resume-from-pause.

Co-Authored-By: Oz <oz-agent@warp.dev>

Author: tbitcs