Add set/get support for foreground, background, cursor, and palette default colors through ghostty_terminal_set and ghostty_terminal_get. Four new set options (COLOR_FOREGROUND, COLOR_BACKGROUND, COLOR_CURSOR, COLOR_PALETTE) write directly to the terminal color defaults. Passing NULL clears the value for RGB colors or resets the palette to the built-in default. All set operations mark the palette dirty flag for the renderer. Eight new get data types retrieve either the effective color (override or default, via DynamicRGB.get) or the default color only (ignoring any OSC overrides). Effective getters for RGB colors return the new NO_VALUE result code when no color is configured. The palette getters return the current or original palette respectively. Adds the GHOSTTY_NO_VALUE result code for cases where a queried value is simply not configured, distinct from GHOSTTY_INVALID_VALUE which indicates a caller error.