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/Badge.tsx

@@ -3,19 +3,19 @@ import type { ReactNode } from "react";
 type Tone = "neutral" | "brand" | "success" | "warning" | "danger" | "info";
 
 const TONE_CLASSES: Record<Tone, string> = {
-  neutral: "bg-gray-800 text-gray-300",
-  brand:   "bg-indigo-900 text-indigo-300",
-  success: "bg-green-900 text-green-300",
-  warning: "bg-yellow-900 text-yellow-300",
-  danger:  "bg-red-900 text-red-300",
-  info:    "bg-blue-900 text-blue-300",
+  neutral: "bg-raised text-ink-2",
+  brand:   "bg-accent/15 text-accent",
+  success: "bg-raised text-ink-2",
+  warning: "bg-sev-moderate/15 text-sev-moderate",
+  danger:  "bg-sev-major/15 text-sev-major",
+  info:    "bg-accent/15 text-accent",
 };
 
 export function Badge({ children, tone = "neutral", className }: { children: ReactNode; tone?: Tone; className?: string }) {
   return (
     <span
       className={[
-        "inline-flex items-center gap-1 text-xs font-mono px-2 py-0.5 rounded-full whitespace-nowrap",
+        "inline-flex items-center gap-1 text-xs font-medium px-2 py-0.5 rounded-full whitespace-nowrap",
         TONE_CLASSES[tone],
         className ?? "",
       ]