PHLEGM v8 adaptive last-good compiler progress

Known-duration compiler progress now uses the previous successful build duration as its basis.

Data-driven defaults in tools/Compiler-UI.json:
- expectedFinishPercent = 95.0
- runningCeilingPercent = 99.9
- overrunTimeConstantBasisMultiples = 1.0

Behavior:
- A current build reaching the previous successful duration reaches expectedFinishPercent, not 100%.
- If it runs longer, progress approaches runningCeilingPercent asymptotically.
- Confirmed success immediately completes the bar at 100% and records the new successful elapsed duration.
- A faster successful build likewise completes immediately and its shorter elapsed duration becomes the next basis.
- Updated in checkpoint 33: Unknown Duration is used only when no successful sample exists; prior failures never invalidate a saved duration average.
- Cancellation does not discard the prior successful duration and does not force Unknown Duration on the next build.
