fix: respawn controller multi-layer detection and cleanup

- Update idle detection from legacy '↵ send' to completion message pattern
  ("for Xm Xs" time patterns like "Worked for 2m 46s")
- Add confirming_idle state for false positive prevention
- Add completionConfirmMs (5s) and noOutputTimeoutMs (30s) config options
- Add multi-layer detection with confidence scoring (0-100%)
- Fix null pointer error in extractTokenCount with guard clause
- Fix respawn controller not stopping on session cleanup (broadcast respawn:stopped)
- Update tests to use new completion message patterns
- Add detection status UI display (confidence level, waiting state)
- Update CLAUDE.md with new detection documentation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/web/public/styles.css

@@ -486,6 +486,44 @@ body {
   font-size: 0.7rem;
 }
 
+.respawn-detection {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+  padding: 0 0.5rem;
+  border-left: 1px solid rgba(34, 197, 94, 0.2);
+}
+
+.detection-status {
+  color: var(--text-muted);
+  font-size: 0.7rem;
+}
+
+.detection-waiting {
+  color: var(--accent);
+  font-size: 0.7rem;
+  font-style: italic;
+}
+
+.detection-confidence {
+  color: var(--text-dim);
+  font-family: 'SF Mono', Monaco, monospace;
+  font-size: 0.65rem;
+  padding: 0.1rem 0.3rem;
+  background: rgba(34, 197, 94, 0.15);
+  border-radius: 3px;
+}
+
+.detection-confidence.high {
+  background: rgba(34, 197, 94, 0.3);
+  color: var(--green);
+}
+
+.detection-confidence.medium {
+  background: rgba(234, 179, 8, 0.2);
+  color: var(--yellow);
+}
+
 @keyframes spin {
   to { transform: rotate(360deg); }
 }