Port the adaptive theme engine from builderbot/staged into sprout. Loads
Shiki theme JSON files (54 themes, lazy-loaded), extracts key colors,
and derives the full shadcn CSS variable palette directly from bg, fg,
comment, and git decoration colors. Light vs dark is auto-detected from
background luminance.
Replace the 3-button toggle with a searchable theme picker. Add a
configurable accent color picker (8 predefined colors) with auto-contrast
foreground calculation, independent of the syntax theme. Default theme is
houston, default accent is blue.
Migrate all hardcoded dark: variants to semantic tokens (text-warning,
text-status-added, text-status-deleted). Cached theme + accent vars
applied synchronously on mount to prevent FOUC.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
