feat(ui): "Graphite & Honey" redesign — warm dark, monospace-first

- new design system in globals.css: warm graphite surfaces, ivory text, honey
  accent; semantic status/data-type/syntax tokens replacing hardcoded colors
- IBM Plex Mono as the universal UI font (sans + mono), tabular numerals
- custom CodeMirror SQL theme (src/lib/editor-theme.ts) matching the palette
- data grid: zebra striping + honey row hover, stronger sticky header
- route status dots, JSON syntax, EXPLAIN cost, schema-tree icons and the
  read/write toggle through the new tokens
- TUSK wordmark in the toolbar

src/components/chat/ChatPanel.tsx

@@ -111,13 +111,13 @@ function UsageBadge({ usage }: { usage: ContextUsage | undefined }) {
 
   let toneClass = "text-muted-foreground/70";
   if (ratio >= 0.85) toneClass = "text-destructive";
-  else if (ratio >= 0.6) toneClass = "text-amber-500";
-  else if (ratio >= 0.3) toneClass = "text-emerald-500/80";
+  else if (ratio >= 0.6) toneClass = "text-warning";
+  else if (ratio >= 0.3) toneClass = "text-success/80";
 
   const trackClass = "h-1.5 w-12 overflow-hidden rounded-full bg-muted";
-  let fillClass = "bg-emerald-500/70";
+  let fillClass = "bg-success/70";
   if (ratio >= 0.85) fillClass = "bg-destructive";
-  else if (ratio >= 0.6) fillClass = "bg-amber-500";
+  else if (ratio >= 0.6) fillClass = "bg-warning";
 
   return (
     <Tooltip>