[editor] Color picker overhaul - recent colors, smart suggestions

- Unified color picker behavior across all panels (text, backgrounds, navigation, theme)

- Always show: recent colors (last 8 used), theme colors, standard presets

- Compact mode for inline use, expanded mode for detailed editing

- Smart suggestions: complementary colors from site theme, high-contrast options against background

**Files:** `src/components/ui/color-picker.tsx`