feat: Implement Gogh Theme Engine with options page, theme parsing, and semantic theme derivation

We're cooked. <skull emoji>

- Added options page for YAML palette editing, live color preview, and diagnostics.
- Implemented theme engine to parse Gogh YAML palettes and derive semantic themes.
- Configured TypeScript and Vite for building the extension.
- Created new tab and popup HTML pages with corresponding scripts and styles.
- Established storage management for user configurations in Chrome storage.
- Added icons for the extension and updated manifest for MV3 compatibility.

gogh-theme-engine/postcss.config.cjs

@@ -0,0 +1,2 @@
+// No PostCSS plugins needed for this project
+module.exports = {};