Phase 4 Stage 0: design system foundation (client_app)

- HaloTokens, HaloSpacing, HaloRadius, HaloMotion, HaloShadows (warm palette;
  calm/playful stubbed for phase 5).
- Bundled Bricolage Grotesque, Poppins, JetBrains Mono (~1.2 MB total, OFL).
- haloThemeData() wired into MaterialApp.router with Figma-aligned text
  scale, pill ElevatedButton, 64px input height, 24px-corner BottomSheet,
  dark pill SnackBar.
- Halo* widget primitives: Button, Orb, StepDots, BottomSheet, Popup,
  Snackbar, Chip.
- Dev-only /_theme_preview route gated by --dart-define=THEME_PREVIEW=true
  for visual reference during stages 2-8.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

client_app/pubspec.yaml

@@ -52,3 +52,21 @@ flutter:
   assets:
     - assets/images/
     - assets/images/splash/
+    - assets/fonts/
+
+  fonts:
+    - family: BricolageGrotesque
+      fonts:
+        - asset: assets/fonts/BricolageGrotesque-Variable.ttf
+    - family: Poppins
+      fonts:
+        - asset: assets/fonts/Poppins-Regular.ttf
+        - asset: assets/fonts/Poppins-Medium.ttf
+          weight: 500
+        - asset: assets/fonts/Poppins-SemiBold.ttf
+          weight: 600
+        - asset: assets/fonts/Poppins-Bold.ttf
+          weight: 700
+    - family: JetBrainsMono
+      fonts:
+        - asset: assets/fonts/JetBrainsMono-Variable.ttf