/**
 * Deep merge utility for theme configuration
 *
 * Performs a recursive deep merge of objects, allowing partial overrides
 * of nested structures like the color palette system.
 *
 * @param target - The base object to merge into
 * @param source - The object to merge from (takes precedence), can be undefined or null
 * @returns A new object with merged values
 *
 * @example
 * // Merge color palettes with partial overrides
 * const defaults = { primary: { 0: '#fff', 100: '#def5ff' } };
 * const custom = { primary: { 100: '#custom' } };
 * const result = deepMerge(defaults, custom);
 * // result.primary = { 0: '#fff', 100: '#custom' }
 */
export declare function deepMerge<T extends Record<string, any> | undefined>(target: T, source?: Record<string, any> | null | undefined): T;