style: fix all golangci-lint issues and format code (refs #17)

Fix 380 lint violations across all Go source files including wsl_v5,
nlreturn, noinlineerr, errcheck, funlen, funcorder, tagliatelle,
perfsprint, modernize, revive, gosec, ireturn, mnd, forcetypeassert,
cyclop, and others.

Key changes:
- Split large handler/command functions into smaller methods
- Extract scan helpers for database queries
- Reorder exported/unexported methods per funcorder
- Add sentinel errors in models package
- Use camelCase JSON tags per tagliatelle defaults
- Add package comments
- Fix .gitignore to not exclude cmd/chat-cli directory

internal/db/db.go

@@ -88,8 +88,10 @@ func NewTest(dsn string) (*Database, error) {
 	}
 
 	// Item 9: Enable foreign keys
-	if _, err := d.Exec("PRAGMA foreign_keys = ON"); err != nil {
+	_, err = d.Exec("PRAGMA foreign_keys = ON") //nolint:noctx // no context in sql.Open path
+	if err != nil {
 		_ = d.Close()
+
 		return nil, fmt.Errorf("enable foreign keys: %w", err)
 	}
 
@@ -162,7 +164,7 @@ func (s *Database) GetChannelByID(
 	return c, nil
 }
 
-// GetUserByNick looks up a user by their nick.
+// GetUserByNickModel looks up a user by their nick.
 func (s *Database) GetUserByNickModel(
 	ctx context.Context,
 	nick string,
@@ -185,7 +187,7 @@ func (s *Database) GetUserByNickModel(
 	return u, nil
 }
 
-// GetUserByToken looks up a user by their auth token.
+// GetUserByTokenModel looks up a user by their auth token.
 func (s *Database) GetUserByTokenModel(
 	ctx context.Context,
 	token string,
@@ -219,6 +221,7 @@ func (s *Database) DeleteAuthToken(
 	_, err := s.db.ExecContext(ctx,
 		`DELETE FROM auth_tokens WHERE token = ?`, token,
 	)
+
 	return err
 }
 
@@ -231,10 +234,11 @@ func (s *Database) UpdateUserLastSeen(
 		`UPDATE users SET last_seen_at = CURRENT_TIMESTAMP WHERE id = ?`,
 		userID,
 	)
+
 	return err
 }
 
-// CreateUser inserts a new user into the database.
+// CreateUserModel inserts a new user into the database.
 func (s *Database) CreateUserModel(
 	ctx context.Context,
 	id, nick, passwordHash string,
@@ -394,6 +398,7 @@ func (s *Database) DequeueMessages(
 	if err != nil {
 		return nil, err
 	}
+
 	defer func() { _ = rows.Close() }()
 
 	entries := []*models.MessageQueueEntry{}
@@ -423,14 +428,14 @@ func (s *Database) AckMessages(
 	}
 
 	placeholders := make([]string, len(entryIDs))
-	args := make([]interface{}, len(entryIDs))
+	args := make([]any, len(entryIDs))
 
 	for i, id := range entryIDs {
 		placeholders[i] = "?"
 		args[i] = id
 	}
 
-	query := fmt.Sprintf(
+	query := fmt.Sprintf( //nolint:gosec // placeholders are ?, not user input
 		"DELETE FROM message_queue WHERE id IN (%s)",
 		strings.Join(placeholders, ","),
 	)
@@ -549,7 +554,8 @@ func (s *Database) connect(ctx context.Context) error {
 	s.log.Info("database connected")
 
 	// Item 9: Enable foreign keys on every connection
-	if _, err := s.db.ExecContext(ctx, "PRAGMA foreign_keys = ON"); err != nil {
+	_, err = s.db.ExecContext(ctx, "PRAGMA foreign_keys = ON")
+	if err != nil {
 		return fmt.Errorf("enable foreign keys: %w", err)
 	}
 
@@ -676,41 +682,54 @@ func (s *Database) applyMigrations(
 			"version", m.version, "name", m.name,
 		)
 
-		tx, err := s.db.BeginTx(ctx, nil)
+		err = s.executeMigration(ctx, m)
 		if err != nil {
-			return fmt.Errorf(
-				"begin tx for migration %d: %w", m.version, err,
-			)
-		}
-
-		_, err = tx.ExecContext(ctx, m.sql)
-		if err != nil {
-			_ = tx.Rollback()
-
-			return fmt.Errorf(
-				"apply migration %d (%s): %w",
-				m.version, m.name, err,
-			)
-		}
-
-		_, err = tx.ExecContext(ctx,
-			"INSERT INTO schema_migrations (version) VALUES (?)",
-			m.version,
-		)
-		if err != nil {
-			_ = tx.Rollback()
-
-			return fmt.Errorf(
-				"record migration %d: %w", m.version, err,
-			)
-		}
-
-		if err := tx.Commit(); err != nil {
-			return fmt.Errorf(
-				"commit migration %d: %w", m.version, err,
-			)
+			return err
 		}
 	}
 
 	return nil
 }
+
+func (s *Database) executeMigration(
+	ctx context.Context,
+	m migration,
+) error {
+	tx, err := s.db.BeginTx(ctx, nil)
+	if err != nil {
+		return fmt.Errorf(
+			"begin tx for migration %d: %w", m.version, err,
+		)
+	}
+
+	_, err = tx.ExecContext(ctx, m.sql)
+	if err != nil {
+		_ = tx.Rollback()
+
+		return fmt.Errorf(
+			"apply migration %d (%s): %w",
+			m.version, m.name, err,
+		)
+	}
+
+	_, err = tx.ExecContext(ctx,
+		"INSERT INTO schema_migrations (version) VALUES (?)",
+		m.version,
+	)
+	if err != nil {
+		_ = tx.Rollback()
+
+		return fmt.Errorf(
+			"record migration %d: %w", m.version, err,
+		)
+	}
+
+	err = tx.Commit()
+	if err != nil {
+		return fmt.Errorf(
+			"commit migration %d: %w", m.version, err,
+		)
+	}
+
+	return nil
+}