fix: 3 critical autonomous engine & mood system bugs

1. Momentum cliff at 10 messages (P0): The conversation momentum formula
   had a discontinuity where the 10th message caused momentum to DROP from
   0.9 to 0.5. Replaced with a smooth log1p curve that monotonically
   increases (0→0→0.20→0.32→...→0.70→0.89→1.0 at 30 msgs).

2. Neutral keywords overriding all moods (P0): detect_mood_shift() checked
   neutral early with generic keywords (okay, sure, hmm) that matched
   almost any response, constantly resetting mood to neutral. Now: all
   specific moods are scored by match count first (best-match wins),
   neutral is only checked as fallback and requires 2+ keyword matches.

3. Uncancellable delayed_wakeup tasks (P0): Fire-and-forget sleep tasks
   could stack and overwrite mood state after manual wake-up. Added a
   centralized wakeup task registry in ServerManager with automatic
   cancellation on manual wake or new sleep cycle.

bot/utils/autonomous_engine.py

@@ -4,6 +4,7 @@ Truly autonomous decision-making engine for Miku.
 Makes decisions based on context signals without constant LLM polling.
 """
 
+import math
 import time
 import random
 from datetime import datetime, timedelta
@@ -203,11 +204,12 @@ class AutonomousEngine:
         ctx.messages_last_hour = sum(1 for t in times if now - t < 3600)
         
         # Calculate conversation momentum (0-1 scale)
-        # High momentum = consistent messages in last 5 minutes
-        if ctx.messages_last_5min >= 10:
-            ctx.conversation_momentum = min(1.0, ctx.messages_last_5min / 20)
+        # Smooth curve: grows quickly at first, then tapers off toward 1.0
+        # 1 msg → 0.10, 5 msgs → 0.41, 10 msgs → 0.63, 20 msgs → 0.82, 40 msgs → 0.95
+        if ctx.messages_last_5min == 0:
+            ctx.conversation_momentum = 0.0
         else:
-            ctx.conversation_momentum = ctx.messages_last_5min / 10
+            ctx.conversation_momentum = min(1.0, math.log1p(ctx.messages_last_5min) / math.log1p(30))
         
         # Time since last action
         if guild_id in self.server_last_action: