feat(bots): anonConfess + shitpostLeaderboard built-in bots

- ConfessBot: polls for /confess messages, deletes original, reposts anonymous
- LeaderboardBot: daily top-10 message count recap from DB
- BotFunc extended with *sql.DB param for DB-reading bots
- Both types registered in runner + BotManager UI

internal/bot/runner.go

@@ -11,8 +11,8 @@ import (
 )
 
 // BotFunc is the signature for a built-in bot type's run function.
-// It blocks until ctx is cancelled. Use send to post messages.
-type BotFunc func(ctx context.Context, config json.RawMessage, send SendMessageFunc)
+// It blocks until ctx is cancelled. Use send to post messages, db to read.
+type BotFunc func(ctx context.Context, db *sql.DB, config json.RawMessage, send SendMessageFunc)
 
 // SendMessageFunc posts a message to a channel as this bot.
 type SendMessageFunc func(channelID, content string)
@@ -91,7 +91,7 @@ func (r *Runner) Start(botID, botType string, config json.RawMessage) {
 				r.logger.Error("bot panic", "bot_id", botID, "type", botType, "panic", rec)
 			}
 		}()
-		fn(ctx, config, send)
+		fn(ctx, r.db, config, send)
 		r.logger.Info("bot stopped", "bot_id", botID, "type", botType)
 	}()
 }