Implement AsciiDoc and TipTap conversion logic, including new Admonition node and CodeBlock extension; add DiffViewer and HistoryPanel components for document version comparison; introduce password hashing utility with SHA-256.

backend/internal/db/db.go

@@ -57,6 +57,13 @@ func (d *DB) init() error {
 	return err
 }
 
+// HasUsers returns true if at least one user account exists.
+func (d *DB) HasUsers() bool {
+	var n int
+	d.sql.QueryRow(`SELECT COUNT(*) FROM users`).Scan(&n)
+	return n > 0
+}
+
 // CreateUser inserts a new user. Returns ErrUserExists if the username is taken.
 func (d *DB) CreateUser(username, passHash, role string) error {
 	_, err := d.sql.Exec(