Studio: refine default theme and add zoom settings

Goal

Refine the studio's default theme to improve visual hierarchy and elegance:

  1. Reduce border contrast — borders are currently too bright compared to the background.
  2. Adjust panel headers — currently too dark; reduce to improve visual balance.
  3. Reduce default font size — smaller fonts are more elegant and fit more content.
  4. Add theme/zoom/font-size controls to the settings panel (#9 (closed)).

Context / integration points

  • DVUI defines the studio's styling (colors, fonts, spacing).
  • Current defaults are functional but visually unpolished.
  • Related to #9 (closed) (settings panel) — settings controls will live there.
  • Affects visual perception of the entire interface.

Design

  • Audit current color scheme: measure contrast ratios, review borders and headers.
  • Adjust color palette: reduce border brightness (or increase background luminosity for balance).
  • Adjust panel header color/saturation for better integration.
  • Reduce default font size by ~10% (e.g., 12px → 11px or similar).
  • Add settings: UI Theme (light/dark/auto), Zoom/Scale (slider 80%-150%), Font Size (slider 90%-120%).

Tasks

  • Audit and document current theme colors
  • Adjust border contrast (reduce brightness or change color tone)
  • Adjust panel header styling
  • Reduce default font size and test readability
  • Add theme/zoom/font-size settings to the settings panel
  • Test the new theme across all panels for visual consistency

Acceptance criteria

  • Borders are visually recessive (not dominating the layout).
  • Panel headers integrate well with the background.
  • Default font size is noticeably smaller but remains readable.
  • Theme/zoom/font-size settings work and persist.

Dependencies

Related to #9 (closed) (settings panel). Can refine theme independently; settings integration requires #9 (closed).

Out of scope

  • Support for user-defined custom themes (future enhancement).
  • Per-panel theme overrides.