feat(web): introduce FabledSword design system tokens + Tailwind aliases

Add the canonical FS token palette (surfaces, text, action, semantic,
accent, radii, fonts) as CSS custom properties under web/src/lib/styles/
fabledsword-tokens.css, with a [data-fs-app="minstrel"] hook reserved
for future per-app accent overrides. Wire the tokens through Tailwind by
aliasing semantic colour utilities (bg-background, bg-surface,
bg-surface-hover, text-text-primary/secondary/muted, border-border,
bg-action-primary/secondary/destructive, accent, warning/error/info) to
the new variables, plus rounded-sm..xl and font-display/sans/mono. Load
Fraunces, Inter, and JetBrains Mono (400/500 only) via Google Fonts and
default the body to Inter. Existing components inherit the new palette
without per-page changes.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/src/app.css

@@ -1,3 +1,5 @@
+@import './lib/styles/fabledsword-tokens.css';
+
 @tailwind base;
 @tailwind components;
 @tailwind utilities;
@@ -11,3 +13,7 @@ body {
   height: 100%;
   margin: 0;
 }
+
+body {
+  font-family: var(--fs-font-body);
+}