Fix all lint/build issues on main branch (closes #13)

- Resolve duplicate method declarations (CreateUser, GetUserByToken,
  GetUserByNick) between db.go and queries.go by renaming queries.go
  methods to CreateSimpleUser, LookupUserByToken, LookupUserByNick
- Fix 377 lint issues across all categories:
  - nlreturn (107): Add blank lines before returns
  - wsl_v5 (156): Add required whitespace
  - noinlineerr (25): Use plain assignments instead of inline error handling
  - errcheck (15): Check all error return values
  - mnd (10): Extract magic numbers to named constants
  - err113 (7): Use wrapped static errors instead of dynamic errors
  - gosec (7): Fix SSRF, SQL injection warnings; add nolint for false positives
  - modernize (7): Replace interface{} with any
  - cyclop (2): Reduce cyclomatic complexity via command map dispatch
  - gocognit (1): Break down complex handler into sub-handlers
  - funlen (3): Extract long functions into smaller helpers
  - funcorder (4): Reorder methods (exported before unexported)
  - forcetypeassert (2): Add safe type assertions with ok checks
  - ireturn (2): Replace interface-returning methods with concrete lookups
  - noctx (3): Use NewRequestWithContext and ExecContext
  - tagliatelle (5): Fix JSON tag casing to camelCase
  - revive (4): Rename package from 'api' to 'chatapi'
  - rowserrcheck (8): Add rows.Err() checks after iteration
  - lll (2): Shorten long lines
  - perfsprint (5): Use strconv and string concatenation
  - nestif (2): Extract nested conditionals into helper methods
  - wastedassign (1): Remove wasted assignments
  - gosmopolitan (1): Add nolint for intentional Local() time display
  - usestdlibvars (1): Use http.MethodGet
  - godoclint (2): Remove duplicate package comments
- Fix broken migration 003_users.sql that conflicted with 002_schema.sql
  (different column types causing test failures)
- All tests pass, make check reports 0 issues

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.ExecContext(context.Background(), "PRAGMA foreign_keys = ON")
+	if err != nil {
 		_ = d.Close()
+
 		return nil, fmt.Errorf("enable foreign keys: %w", err)
 	}
 
@@ -219,6 +221,7 @@ func (s *Database) DeleteAuthToken(
 	_, err := s.db.ExecContext(ctx,
 		`DELETE FROM auth_tokens WHERE token = ?`, token,
 	)
+
 	return err
 }
 
@@ -231,6 +234,7 @@ func (s *Database) UpdateUserLastSeen(
 		`UPDATE users SET last_seen_at = CURRENT_TIMESTAMP WHERE id = ?`,
 		userID,
 	)
+
 	return err
 }
 
@@ -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 // G201: placeholders are literal "?" strings, 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)
 	}
 
@@ -671,46 +677,56 @@ func (s *Database) applyMigrations(
 			continue
 		}
 
-		s.log.Info(
-			"applying migration",
-			"version", m.version, "name", m.name,
-		)
-
-		tx, err := s.db.BeginTx(ctx, nil)
+		err = s.applySingleMigration(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) applySingleMigration(ctx context.Context, m migration) error {
+	s.log.Info(
+		"applying migration",
+		"version", m.version, "name", m.name,
+	)
+
+	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
+}