style(frontend): look&feel v2 — layered shadows, sharper radii, mono data register

Colors (GSD palette) untouched. New visual vocabulary across the whole GUI:
- warm-tinted layered shadow tokens (--shadow-xs/sm/md) replacing flat rings;
  cards/dialogs framed with hairline border + real elevation
- strict radii scale: xl cards / lg inputs / md controls / 2xl dialogs;
  buttons move from pills to rounded-md
- third type register: --font-mono + tabular-nums on SQL, timers, dates, ids;
  standardized .thot-label micro-label tier
- prose: framed tables with uppercase headers, elevated code blocks
- SqlViewer badges moved from hardcoded Tailwind greens/reds to success/
  destructive token tints; ResultsPanel inline styles replaced with classes
- artifact gate: first option rendered as filled primary action

Verified offline via Playwright against a mock backend replaying a real psd
session (no VPN needed). tsc clean, 115/115 vitest.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/shell/ModelActivityPanel.tsx

@@ -31,7 +31,7 @@ export function ModelActivityPanel({ onClose }: { onClose: () => void }) {
 
   return (
     <aside className="flex w-[30vw] max-w-[30vw] shrink-0 flex-col border-r border-border bg-sidebar">
-      <div className="flex items-center justify-between border-b border-border/70 px-3 py-3">
+      <div className="flex items-center justify-between border-b border-border/60 px-3 py-3">
         <h2 className="font-heading text-sm font-semibold text-foreground">Model activity</h2>
         <div className="flex items-center gap-1">
           {canExpand && (