Cline web visual foundation

The shared visual contract now lives in the internal @cline/ui workspace package instead of beside the desktop app.

The desktop imports the complete @cline/ui/theme/index.css entry point. Other Cline surfaces can import @cline/ui/theme/tokens.css without React or Tailwind, or compose the Tailwind adapter and optional base styles in order. Consuming apps still own their font files and shell-specific layout.