bundle JetBrains Mono for terminal panes

Vendor the 4 core weights (Regular, Italic, Bold, BoldItalic) of
JetBrains Mono v2.304 under app/assets/fonts/jetbrains_mono/, ~1 MB
total. OFL license checked in alongside. Declared as the
JetBrainsMono family in pubspec so Flutter bundles it automatically.

app/lib/widgets/src/typography.dart exposes clideMonoFamily plus a
platform-ordered fallback chain (SF Mono / Menlo / Monaco →
JetBrains Mono system install / Fira Code / Hack / DejaVu / Liberation →
Cascadia / Consolas → monospace) for web builds and test harnesses
that don't load asset fonts. Terminal widgets pick both up via a
single import.

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

app/lib/widgets/src/typography.dart

@@ -0,0 +1,32 @@
+/// Typography constants shared across widgets.
+///
+/// Terminal panes, diff views, and any other monospace surface should
+/// import from here rather than hardcoding a family. The fallback chain
+/// exists for web builds + platforms where the bundled `JetBrainsMono`
+/// asset isn't picked up (rare, but possible during `flutter test` if
+/// assets aren't declared in the harness).
+library;
+
+/// The bundled monospace family. Always resolved first.
+const String clideMonoFamily = 'JetBrainsMono';
+
+/// System fallback chain. Ordered by platform prevalence + quality of
+/// programming-ligature / box-drawing coverage.
+const List<String> clideMonoFamilyFallback = [
+  // macOS
+  'SF Mono',
+  'Menlo',
+  'Monaco',
+  // Linux
+  'JetBrains Mono',  // if the user has it system-installed under the
+                     // canonical PostScript name
+  'Fira Code',
+  'Hack',
+  'DejaVu Sans Mono',
+  'Liberation Mono',
+  // Windows
+  'Cascadia Code',
+  'Consolas',
+  // Last resort
+  'monospace',
+];