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/memory/MemoryPanel.tsx

@@ -131,7 +131,7 @@ export function MemoryPanel() {
       )}
 
       {dirty && (
-        <div className="border-t border-border/40 px-3 py-1.5 text-[10px] text-amber-500/80">
+        <div className="border-t border-border/40 px-3 py-1.5 text-[10px] text-warning/80">
           Unsaved changes
         </div>
       )}