refactor: extract sentiment cog into package with shared _process_finding

Convert cogs/sentiment.py (1050 lines) into cogs/sentiment/ package:
- __init__.py (656 lines): core SentimentCog with new _process_finding()
  that deduplicates the per-user finding loop from _process_buffered and
  _run_mention_scan (~90 lines each → single shared method)
- actions.py: mute_user, warn_user
- topic_drift.py: handle_topic_drift
- channel_redirect.py: handle_channel_redirect, build_channel_context
- coherence.py: handle_coherence_alert
- log_utils.py: log_analysis, log_action, score_color
- state.py: save_user_state, flush_dirty_states

All extracted modules use plain async functions (not methods) receiving
bot/config as parameters. Named log_utils.py to avoid shadowing stdlib
logging. Also update CLAUDE.md with comprehensive project documentation.

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

cogs/sentiment/state.py

@@ -0,0 +1,41 @@
+import asyncio
+import logging
+
+logger = logging.getLogger("bcs.sentiment")
+
+
+def save_user_state(bot, dirty_users: set[int], user_id: int) -> None:
+    """Fire-and-forget save of a user's current state to DB."""
+    user_data = bot.drama_tracker.get_user(user_id)
+    asyncio.create_task(bot.db.save_user_state(
+        user_id=user_id,
+        offense_count=user_data.offense_count,
+        immune=user_data.immune,
+        off_topic_count=user_data.off_topic_count,
+        baseline_coherence=user_data.baseline_coherence,
+        user_notes=user_data.notes or None,
+        warned=user_data.warned_since_reset,
+        last_offense_at=user_data.last_offense_time or None,
+    ))
+    dirty_users.discard(user_id)
+
+
+async def flush_dirty_states(bot, dirty_users: set[int]) -> None:
+    """Save all dirty user states to DB."""
+    if not dirty_users:
+        return
+    dirty = list(dirty_users)
+    dirty_users.clear()
+    for user_id in dirty:
+        user_data = bot.drama_tracker.get_user(user_id)
+        await bot.db.save_user_state(
+            user_id=user_id,
+            offense_count=user_data.offense_count,
+            immune=user_data.immune,
+            off_topic_count=user_data.off_topic_count,
+            baseline_coherence=user_data.baseline_coherence,
+            user_notes=user_data.notes or None,
+            warned=user_data.warned_since_reset,
+            last_offense_at=user_data.last_offense_time or None,
+        )
+    logger.info("Flushed %d dirty user states to DB.", len(dirty))