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/index.html

@@ -65,6 +65,11 @@
     <div class="respawn-banner" id="respawnBanner" style="display: none;">
       <span class="respawn-indicator">&#x21BB;</span>
       <span class="respawn-state" id="respawnState">Watching</span>
+      <span class="respawn-detection" id="respawnDetection">
+        <span class="detection-status" id="detectionStatus"></span>
+        <span class="detection-waiting" id="detectionWaiting"></span>
+        <span class="detection-confidence" id="detectionConfidence"></span>
+      </span>
       <span class="respawn-cycles">Cycle <span id="respawnCycleCount">0</span></span>
       <span class="respawn-timer" id="respawnTimer" style="display: none;"></span>
       <span class="respawn-tokens" id="respawnTokens" style="display: none;"></span>