feat: move user aliases from config to DB with /bcs-alias command

Aliases now stored in UserState table instead of config.yaml. Adds
Aliases column (NVARCHAR 500), loads on startup, persists via flush.
New /bcs-alias slash command (view/set/clear) for managing nicknames.

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

cogs/sentiment/state.py

@@ -4,6 +4,11 @@ import logging
 logger = logging.getLogger("bcs.sentiment")
 
 
+def _aliases_csv(user_data) -> str | None:
+    """Convert aliases list to comma-separated string for DB storage."""
+    return ",".join(user_data.aliases) if user_data.aliases else None
+
+
 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)
@@ -16,6 +21,7 @@ def save_user_state(bot, dirty_users: set[int], user_id: int) -> None:
         user_notes=user_data.notes or None,
         warned=user_data.warned_since_reset,
         last_offense_at=user_data.last_offense_time or None,
+        aliases=_aliases_csv(user_data),
     ))
     dirty_users.discard(user_id)
 
@@ -37,5 +43,6 @@ async def flush_dirty_states(bot, dirty_users: set[int]) -> None:
             user_notes=user_data.notes or None,
             warned=user_data.warned_since_reset,
             last_offense_at=user_data.last_offense_time or None,
+            aliases=_aliases_csv(user_data),
         )
     logger.info("Flushed %d dirty user states to DB.", len(dirty))