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/log_utils.py

@@ -0,0 +1,54 @@
+import logging
+
+import discord
+
+logger = logging.getLogger("bcs.sentiment")
+
+
+def score_color(score: float) -> discord.Color:
+    if score >= 0.75:
+        return discord.Color.red()
+    if score >= 0.6:
+        return discord.Color.orange()
+    if score >= 0.3:
+        return discord.Color.yellow()
+    return discord.Color.green()
+
+
+async def log_analysis(
+    message: discord.Message, score: float, drama_score: float,
+    categories: list[str], reasoning: str, off_topic: bool, topic_category: str,
+):
+    log_channel = discord.utils.get(
+        message.guild.text_channels, name="bcs-log"
+    )
+    if not log_channel:
+        return
+
+    # Only log notable messages (score > 0.1) to avoid spam
+    if score <= 0.1:
+        return
+
+    cat_str = ", ".join(c for c in categories if c != "none") or "none"
+    embed = discord.Embed(
+        title=f"Analysis: {message.author.display_name}",
+        description=f"#{message.channel.name}: {message.content[:200]}",
+        color=score_color(score),
+    )
+    embed.add_field(name="Message Score", value=f"{score:.2f}", inline=True)
+    embed.add_field(name="Rolling Drama", value=f"{drama_score:.2f}", inline=True)
+    embed.add_field(name="Categories", value=cat_str, inline=True)
+    embed.add_field(name="Reasoning", value=reasoning[:1024] or "n/a", inline=False)
+    try:
+        await log_channel.send(embed=embed)
+    except discord.HTTPException:
+        pass
+
+
+async def log_action(guild: discord.Guild, text: str):
+    log_channel = discord.utils.get(guild.text_channels, name="bcs-log")
+    if log_channel:
+        try:
+            await log_channel.send(text)
+        except discord.HTTPException:
+            pass