Add switchable bot modes: default, chatty, and roast

Adds a server-wide mode system with /bcs-mode command.
- Default: current hall-monitor behavior unchanged
- Chatty: friendly chat participant with proactive replies (~10% chance)
- Roast: savage roast mode with proactive replies
- Chatty/roast use relaxed moderation thresholds
- 5-message cooldown between proactive replies per channel
- Bot status updates to reflect active mode
- /bcs-status shows current mode and effective thresholds

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

config.yaml

@@ -46,6 +46,44 @@ messages:
   topic_owner_dm: "Heads up: {username} keeps going off-topic with personal drama in #{channel}. They've been reminded {count} times. Might need a word."
   channel_redirect: "Hey {username}, that sounds like {game} talk — head over to {channel} for that!"
 
+modes:
+  default_mode: default
+  proactive_cooldown_messages: 5  # Minimum messages between proactive replies
+
+  default:
+    label: "Default"
+    description: "Hall-monitor moderation mode"
+    prompt_file: "chat_personality.txt"
+    proactive_replies: false
+    reply_chance: 0.0
+    moderation: full
+
+  chatty:
+    label: "Chatty"
+    description: "Friendly chat participant"
+    prompt_file: "chat_chatty.txt"
+    proactive_replies: true
+    reply_chance: 0.10
+    moderation: relaxed
+    relaxed_thresholds:
+      warning_threshold: 0.80
+      mute_threshold: 0.85
+      spike_warning_threshold: 0.70
+      spike_mute_threshold: 0.85
+
+  roast:
+    label: "Roast"
+    description: "Savage roast mode"
+    prompt_file: "chat_roast.txt"
+    proactive_replies: true
+    reply_chance: 0.10
+    moderation: relaxed
+    relaxed_thresholds:
+      warning_threshold: 0.85
+      mute_threshold: 0.90
+      spike_warning_threshold: 0.75
+      spike_mute_threshold: 0.90
+
 coherence:
   enabled: true
   drop_threshold: 0.3       # How far below baseline triggers alert