The editor ships its own font, Source Sans 3 and Code Pro (#202)

Theme named Inter and JetBrains Mono, but neither was ever shipped,
so every machine drew the editor in whatever it had installed. The
e2e runs measured text in a different face than the user saw.

- Five Latin woff2 faces live in src/ui/fonts/ next to their OFL
  licences: Source Sans 3 400/500/600/700 and Source Code Pro 400.
- fonts.ts loads them through FontFace, and main.ts waits for them
  before the first widget exists, so Pixi measures the real face.
- A face that fails to load is reported in the console and the
  system fallback in Theme takes over.
- Theme is retuned by hand: 12 px body, 22 px rows, smaller gaps
  and padding, radius 8, and weight 500 for bold and headings.
- The scene background default follows Theme.colors.graphBackground.
  This makes core import from ui for the first time.

Findings:
- The 500 file is in the folder but fonts.ts does not register it
  yet, so weight 500 currently falls back to the 400 face.

Tests:
- ./check.sh: 141 files, 2080 tests, exit 0.
- e2e not run. Checks that measure widths or row positions are
  expected to need updating for the new metrics.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/ui/Theme.ts

@@ -2,21 +2,22 @@
 import { TextStyle } from 'pixi.js';
 
 export const Theme = {
-  font: 'Inter, "Segoe UI", Roboto, Helvetica, Arial, sans-serif',
-  monoFont: '"JetBrains Mono", Consolas, "Courier New", monospace',
-  fontSize: 13,
+  // Both ship with the build (`fonts.ts`); the rest only covers glyphs outside their Latin subset.
+  font: '"Source Sans 3", "Segoe UI", Roboto, Helvetica, Arial, sans-serif',
+  monoFont: '"Source Code Pro", Consolas, "Courier New", monospace',
+  fontSize: 12,
   smallFontSize: 11,
   viewportLabelSize: 10,
-  rowHeight: 26,
+  rowHeight: 22,
   controlHeight: 24,
   padding: 8,
-  gap: 6,
-  radius: 4,
-  fieldPadding: 6,
+  gap: 4,
+  radius: 8,
+  fieldPadding: 4,
   checkboxSize: 16,
-  scrollbarWidth: 6,
+  scrollbarWidth: 4,
   /** Horizontal indent per nesting level in tree lists. */
-  treeIndent: 14,
+  treeIndent: 12,
   hoverCursor: 'default',
   colors: {
     background: 0x1b1d22,
@@ -108,7 +109,7 @@ export function textStyle(token: TextStyleToken = 'body'): TextStyle {
       style = new TextStyle(base);
       break;
     case 'bodyBold':
-      style = new TextStyle({ ...base, fontWeight: '600' });
+      style = new TextStyle({ ...base, fontWeight: '500' });
       break;
     case 'muted':
       style = new TextStyle({ ...base, fill: Theme.colors.textMuted });
@@ -129,7 +130,7 @@ export function textStyle(token: TextStyleToken = 'body'): TextStyle {
       style = new TextStyle({
         ...base,
         fontSize: Theme.smallFontSize,
-        fontWeight: '700',
+        fontWeight: '500',
         letterSpacing: 0.5,
         fill: Theme.colors.textMuted,
       });