Expose theme colors as values and add theme.style() for combined styling.
- @earendil-works/pi-tui gains a Color type (palette index, sRGB, OKLCH) with parseColor(), mixColors(), colorToHex(), colorToRgb(), styleText() and related helpers.
- Theme JSON accepts #rgb and oklch(...) values and an optional appearance ("dark" or "light"), detected from the theme colors when omitted.
- theme.style() combines tokens or concrete colors with text attributes; theme.colors exposes concrete colors, including the terminal's reported default colors (OSC 10/11) for tokens set to "".
- Terminals with TERM=*-direct are detected as truecolor.
Reuse the stable renderer, viewport layout, theme detection, and terminal appearance updates. Keep successful operation status derived from replicated lane state.
- add `--use-theme` for fixed and terminal-aware theme pairs
- keep invocation state non-persistent until an explicit selection
- preserve active themes across previews, reloads, and HTML exports
