Frontend redesign chunk 2: primitives and marks

Rewrite components/ui/* (Button, Card, Badge, PageHeader, EmptyState,
Skeleton) against the chunk-1 tokens instead of hardcoded gray-9xx classes,
and drop the remaining font-mono from label/heading text.

Add the three colour-blindness-validated encoding components from
UI_REDESIGN.md §2.3:
- components/marks/SeverityMark.tsx — glyph (filled triangle / outline
  triangle / outline circle) + optional spine + optional label, from the
  four-level severity ladder. Colour is never the only channel.
- components/marks/TypeGlyph.tsx — five stroked SVG glyphs (fire, police,
  ems, collision, other) in currentColor. Incident type is now shape, not
  hue, since five hues can't clear an all-pairs CVD gate.
- components/marks/NodeMark.tsx — diamond at four weights (filled+ring /
  filled / hollow / hollow-dashed). Green is gone from node state entirely.

lib/severity.tsx now renders through SeverityMark; SEVERITY_COLORS reads
the validated sev-moderate/sev-major tokens with routine/minor neutral.
IncidentBadges.tsx's TypeBadge is reimplemented on TypeGlyph instead of a
coloured pill.

Per UI_REDESIGN.md chunk 2.

drb-frontend/components/ui/Button.tsx

@@ -6,13 +6,13 @@ type Size = "sm" | "md" | "lg";
 
 const VARIANT_CLASSES: Record<Variant, string> = {
   primary:
-    "bg-indigo-600 hover:bg-indigo-500 active:bg-indigo-700 text-white shadow-card disabled:hover:bg-indigo-600",
+    "bg-accent hover:brightness-110 active:brightness-95 text-white shadow-card disabled:hover:brightness-100",
   secondary:
-    "bg-gray-800 hover:bg-gray-700 active:bg-gray-700 text-gray-100 border border-gray-700 disabled:hover:bg-gray-800",
+    "bg-raised hover:brightness-110 active:brightness-95 text-ink border border-line disabled:hover:brightness-100",
   ghost:
-    "bg-transparent hover:bg-gray-800 active:bg-gray-800 text-gray-300 hover:text-white disabled:hover:bg-transparent",
+    "bg-transparent hover:bg-raised active:bg-raised text-ink-2 hover:text-ink disabled:hover:bg-transparent",
   danger:
-    "bg-red-700 hover:bg-red-600 active:bg-red-700 text-white disabled:hover:bg-red-700",
+    "bg-sev-major hover:brightness-110 active:brightness-95 text-white disabled:hover:brightness-100",
 };
 
 const SIZE_CLASSES: Record<Size, string> = {
@@ -24,7 +24,7 @@ const SIZE_CLASSES: Record<Size, string> = {
 const BASE =
   "inline-flex items-center justify-center font-semibold transition-colors " +
   "disabled:opacity-50 disabled:cursor-not-allowed " +
-  "focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-indigo-500 focus-visible:ring-offset-2 focus-visible:ring-offset-gray-950";
+  "focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-accent focus-visible:ring-offset-2 focus-visible:ring-offset-page";
 
 interface CommonProps {
   variant?: Variant;