fix(#695): Add crisis hook module for 988 Lifeline integration

Creates agent/crisis_hook.py with:
- CrisisSeverity enum
- detect_crisis() pattern matching
- get_crisis_response() with 988 info
- check_crisis() convenience function

Refs #695

agent/crisis_hook.py

@@ -0,0 +1,85 @@
+"""
+Crisis Detection Hook — Integrates 988 Lifeline into conversation loop.
+
+When crisis is detected in user messages, returns 988 Lifeline
+information immediately instead of processing the original request.
+"""
+
+import re
+import logging
+from dataclasses import dataclass
+from enum import Enum
+from typing import Optional, Tuple
+
+logger = logging.getLogger(__name__)
+
+
+class CrisisSeverity(Enum):
+    NONE = 0
+    MODERATE = 1
+    HIGH = 2
+    CRITICAL = 3
+
+
+@dataclass
+class CrisisDetection:
+    detected: bool
+    severity: CrisisSeverity
+    matched_patterns: list
+    confidence: float
+
+
+# Crisis detection patterns
+_CRISIS_PATTERNS = [
+    (r"\b(i want to die|want to kill myself|end (my|it all))\b", CrisisSeverity.CRITICAL, 0.95),
+    (r"\b(kill(ing)? myself|suicide|suicidal)\b", CrisisSeverity.CRITICAL, 0.90),
+    (r"\b(no reason to live|don'?t want to (live|be here|exist))\b", CrisisSeverity.HIGH, 0.85),
+    (r"\b(better off (dead|without me)|wish i was dead)\b", CrisisSeverity.HIGH, 0.85),
+    (r"\b(can'?t go on|can'?t take (it|this) anymore)\b", CrisisSeverity.HIGH, 0.80),
+    (r"\b(self[- ]?harm|cut(ting)? myself|hurt(ing)? myself)\b", CrisisSeverity.HIGH, 0.85),
+    (r"\b(hopeless|no hope|give up on (life|everything))\b", CrisisSeverity.MODERATE, 0.70),
+]
+
+_COMPILED = [(re.compile(p, re.IGNORECASE), s, c) for p, s, c in _CRISIS_PATTERNS]
+
+
+def detect_crisis(message: str) -> CrisisDetection:
+    if not message or not isinstance(message, str):
+        return CrisisDetection(False, CrisisSeverity.NONE, [], 0.0)
+    
+    matched = []
+    max_severity = CrisisSeverity.NONE
+    max_confidence = 0.0
+    
+    for pattern, severity, confidence in _COMPILED:
+        if pattern.search(message):
+            matched.append(pattern.pattern)
+            if confidence > max_confidence:
+                max_confidence = confidence
+            if severity.value > max_severity.value:
+                max_severity = severity
+    
+    detected = len(matched) > 0
+    return CrisisDetection(detected, max_severity, matched, max_confidence)
+
+
+def get_crisis_response(severity: str = "CRITICAL") -> str:
+    return """I hear you, and you are not alone.
+
+**Please reach out for help right now:**
+
+📞 **Call 988** — Suicide & Crisis Lifeline (24/7)
+💬 **Text HOME to 988** — Crisis text line
+🌐 **Chat:** 988lifeline.org/chat
+🇪🇸 **Spanish:** 1-888-628-9454
+🎖️ **Veterans:** 988, then press 1
+
+You don\'t have to face this alone. Please hold on."""
+
+
+def check_crisis(user_message: str) -> Optional[str]:
+    detection = detect_crisis(user_message)
+    if detection.detected:
+        logger.warning("Crisis detected: severity=%s", detection.severity.name)
+        return get_crisis_response(detection.severity.name)
+    return None