Messages: Add archive (soft-delete) support + dropdown UI polish

- Implemented `/account/messages/archive` route for soft-archiving messages
- Added `is_archived` flag to `users_messages` schema and model
- Topbar dropdown now reflects accurate unread message count
- Fixed missing route registration for archive handler
- Improved message visibility checks to prevent access violations
- Placeholder for rate-limit (429) error page rendering identified

storage/messages.go

@@ -10,7 +10,7 @@ func GetMessageCount(db *sql.DB, userID int) (int, error) {
 	var count int
 	err := db.QueryRow(`
 		SELECT COUNT(*) FROM users_messages 
-		WHERE recipientId = ? AND is_read = FALSE
+		WHERE recipientId = ? AND is_read = FALSE AND is_archived = FALSE
 	`, userID).Scan(&count)
 	return count, err
 }
@@ -19,7 +19,7 @@ func GetRecentMessages(db *sql.DB, userID int, limit int) []models.Message {
 	rows, err := db.Query(`
 		SELECT id, senderId, recipientId, subject, message, is_read, created_at
 		FROM users_messages
-		WHERE recipientId = ?
+		WHERE recipientId = ? AND is_archived = FALSE
 		ORDER BY created_at DESC
 		LIMIT ?
 	`, userID, limit)
@@ -81,3 +81,12 @@ func MarkMessageAsRead(db *sql.DB, messageID, userID int) error {
 	}
 	return nil
 }
+
+func ArchiveMessage(db *sql.DB, userID, messageID int) error {
+	_, err := db.Exec(`
+		UPDATE users_messages
+		SET is_archived = TRUE
+		WHERE id = ? AND recipientId = ?
+	`, messageID, userID)
+	return err
+}