perf: rate limiter cleanup goroutine, DB pool constraints

- ipLimiter evicts stale entries after 10 min of inactivity via 5 min sweep
- DB pool capped at 25 max open, 5 idle, 15 min lifetime

internal/db/db.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"database/sql"
 	"fmt"
+	"time"
 
 	"git.dustin.coffee/hobokenchicken/dumpsterChat/internal/config"
 
@@ -24,6 +25,11 @@ func New(cfg *config.Config) (*DB, error) {
 		return nil, fmt.Errorf("ping database: %w", err)
 	}
 
+	// ponytail: prevent unbounded connection growth under burst load
+	db.SetMaxOpenConns(25)
+	db.SetMaxIdleConns(5)
+	db.SetConnMaxLifetime(15 * time.Minute)
+
 	return &DB{db}, nil
 }