feat(web): design tokens, Tailwind config, base components (TEC-3057)

- Add chart palette, motion, and z-index CSS vars to globals.css
- Replace custom theme-provider with next-themes (dark default)
- Extend tailwind.config.ts with heading fonts, spacing (row-compact,
  row-roomy, sidebar), chart colors, elevation shadows, glow shadows,
  transition timing, pill border-radius, z-index scale
- Update tick-flash animations to match design token spec (480ms)
- Add prefers-reduced-motion support for all animations
- Create base design-system components:
  Surface, SurfaceElevated, Divider, DensityProvider/useDensity,
  Numeric (VND/percent/compact formatting), Signal (up/down/neutral pill)
- Add dev-only /dev/tokens showcase route (404 in production)
- Update theme-provider tests to match next-themes integration

Co-Authored-By: Paperclip <noreply@paperclip.ing>

pnpm-lock.yaml

@@ -334,6 +334,9 @@ importers:
       next-intl:
         specifier: ^4.9.0
         version: 4.9.0(next@15.5.15(@babel/core@7.29.0)(@opentelemetry/api@1.9.1)(@playwright/test@1.59.1)(react-dom@18.3.1(react@18.3.1))(react@18.3.1))(react@18.3.1)(typescript@6.0.2)
+      next-themes:
+        specifier: ^0.4.6
+        version: 0.4.6(react-dom@18.3.1(react@18.3.1))(react@18.3.1)
       react:
         specifier: ^18.3.0
         version: 18.3.1
@@ -5639,6 +5642,12 @@ packages:
       typescript:
         optional: true
 
+  next-themes@0.4.6:
+    resolution: {integrity: sha512-pZvgD5L0IEvX5/9GWyHMf3m8BKiVQwsCMHfoFosXtXBMnaS0ZnIJ9ST4b4NqLVKDEm8QBxoNNGNaBv2JNF6XNA==}
+    peerDependencies:
+      react: ^16.8 || ^17 || ^18 || ^19 || ^19.0.0-rc
+      react-dom: ^16.8 || ^17 || ^18 || ^19 || ^19.0.0-rc
+
   next@15.5.15:
     resolution: {integrity: sha512-VSqCrJwtLVGwAVE0Sb/yikrQfkwkZW9p+lL/J4+xe+G3ZA+QnWPqgcfH1tDUEuk9y+pthzzVFp4L/U8JerMfMQ==}
     engines: {node: ^18.18.0 || ^19.8.0 || >= 20.0.0}
@@ -13181,6 +13190,11 @@ snapshots:
     transitivePeerDependencies:
       - '@swc/helpers'
 
+  next-themes@0.4.6(react-dom@18.3.1(react@18.3.1))(react@18.3.1):
+    dependencies:
+      react: 18.3.1
+      react-dom: 18.3.1(react@18.3.1)
+
   next@15.5.15(@babel/core@7.29.0)(@opentelemetry/api@1.9.1)(@playwright/test@1.59.1)(react-dom@18.3.1(react@18.3.1))(react@18.3.1):
     dependencies:
       '@next/env': 15.5.15