feat(ui): design-system foundation — shared token layer + fonts

Establish the visual-redesign foundation (task group 1): a single
shared source of design tokens both apps consume, so Planner and
Journal read from one palette/typography layer instead of drifting
per-app.

- New @trails-cool/ui package exporting theme.css: Tailwind v4 @theme
  tokens (warm off-white surfaces, one sage accent, earthy overnight
  tones, elevation-gradient colors, shadows) extracted from the
  visual-redesign mockup.
- Self-hosted Outfit (body) + Geist Mono (stats) via @fontsource-variable
  — privacy-first, no Google Fonts CDN.
- Both apps import the theme and set the base canvas to the warm
  off-white token + Outfit as the default font.

Foundation only: tokens are now available as Tailwind utilities
(bg-bg-raised, text-accent, font-mono, …) and raw CSS vars. Wiring
them into specific surfaces (topbar, sidebar, markers, elevation
chart) is later task groups.

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

apps/planner/package.json

@@ -28,6 +28,7 @@
     "@trails-cool/i18n": "workspace:*",
     "@trails-cool/jobs": "workspace:*",
     "@trails-cool/map-core": "workspace:*",
+    "@trails-cool/ui": "workspace:*",
     "@trails-cool/sentry-config": "workspace:*",
     "@trails-cool/types": "workspace:*",
     "codemirror": "^6.0.2",