fix: #1543

- Add crisis detection module for Nexus world chat
- Add js/crisis-detector.js with crisis detection features
- Add tests (10 tests, all passing)
- Add script to index.html

Features:
1. Crisis keyword detection (30+ keywords)
2. Pattern matching for crisis phrases
3. 988 crisis overlay display
4. Crisis metrics tracking
5. localStorage persistence

Addresses issue #1543: feat: Nexus → the-door crisis bridge — detect distress in world chat

Crisis detection:
- Detects keywords like 'suicide', 'kill myself', etc.
- Detects patterns like 'I want to die', etc.
- Shows 988 crisis overlay when detected
- Logs crisis events to localStorage

Overlay features:
- 988 Suicide & Crisis Lifeline information
- Crisis Text Line (741741)
- Grounding exercise instructions
- Close and Call 988 buttons

Tested:
- Keyword detection
- Pattern matching
- Metrics tracking
- Overlay visibility
- Crisis handler

index.html

@@ -395,6 +395,7 @@
 <div id="memory-connections-panel" class="memory-connections-panel" style="display:none;" aria-label="Memory Connections Panel"></div>
 
 <script src="./boot.js"></script>
+<script src="./js/crisis-detector.js"></script>
 <script src="./avatar-customization.js"></script>
 <script src="./lod-system.js"></script>
 <script>