feat(statusbar): icon toggles, taller bar, centered pills (#216)

The bottom status bar was hard to read: size-10 text labels in a 26px
strip. Make it legible and consistent with the drawing tab bar:

- Height 26 → 30 to match the document tab bar; the command-line input
  pill matches too, so the three strips line up.
- Replace the drafting-aid toggle labels (ORTHO/POLAR/OSNAP/OTRACK/DYN/
  LWT and the OCS pills ISO/QP/FILTER/SC/CLEAN/TPY) with 17px SVG icons;
  the name stays in each pill's tooltip. Twelve new icons under
  assets/icons/status, drawn in the existing 24×24 stroke style.
- Vertically centre every element via center_y, and bump all pill text to
  size 12 with uniform padding plus larger chrome icons (menu, scroll
  arrows, osnap dropdown) so nothing reads smaller than the toggle icons.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

assets/icons/status/cleanscreen.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="#000000" stroke-width="1.8" stroke-linecap="round" stroke-linejoin="round"><path d="M4 9 V4 H9 M15 4 H20 V9 M20 15 V20 H15 M9 20 H4 V15"/></svg>