- Reduce themes from 6 to 4: system, light, dark, paper
  - Remove midnight (too similar to dark) and whitewall (too similar to light)
  - Drop all unused tokens: chart-*, sidebar-primary, sidebar-border,
    sidebar-ring, shadow-2xs, tracking-normal, spacing
  - Remove redundant @theme inline blocks from dynamic theme files
    (Tailwind only processes them at compile time, not at runtime)
  - Move shared tokens (fonts, radius) to default.css only

- Polish dark mode color palette
  - Consistent cool-slate hue (h265) across all surfaces
  - Proper surface layering: sidebar(0.07) → bg(0.09) → card(0.13) →
    popover(0.17) → secondary(0.19) → muted(0.21) → accent(0.22)
  - Foreground softened to 0.82 (from 0.9) — comfortable off-white
  - Accent more chromatic than muted (0.012 vs 0.008) — hover feels interactive
  - Popover elevated above card (0.17 vs 0.13) — floating elements visible
  - Destructive more vivid (0.62/c0.20) — clearly red on dark surfaces
  - Input border (0.25) more distinct than layout border (0.21)
  - Sidebar foreground (0.68) dimmer than content foreground (0.82)

- Fix inline code background invisible in dark mode (#5674)
  - Muted was same lightness as card — increased to 0.21 for clear contrast