feat(tui): add compaction probe metrics to TUI dashboard #2049
Description
Display compaction probe statistics in TUI metrics panel.
Related to: PR #2047 (compaction probe validation #1609)
Phase: 3 (post-MVP integration)
Add to metrics widget:
- Last probe verdict (Pass/SoftFail/HardFail/Error)
- Last probe score (f32)
- Probe pass rate (% of total probes)
- Soft failure rate
- Hard failure rate
- Error count
Panel layout: row under compression metrics showing: Probe: [Pass 87% | SoftFail 10% | HardFail 2% | Error 1%] | Last: Pass (0.78)
Design note: Follow existing metrics panel patterns (MetricsCollector, watch channel, render callback).