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/CentralStatus.tsx

@@ -46,7 +46,7 @@ export function CentralStatus({ working }: { working: boolean }) {
     <div className="flex flex-col gap-3">
       {lastUserEntry && (
         <div className="rounded-lg border border-border/70 bg-card px-3 py-2">
-          <span className="text-[0.65rem] font-semibold uppercase tracking-wide text-muted-foreground">
+          <span className="thot-label">
             {lastUserEntry.kind === "input" ? "You asked" : "You chose"}
           </span>
           <p className="mt-0.5 text-sm text-foreground">{lastUserEntry.text}</p>
@@ -61,11 +61,11 @@ export function CentralStatus({ working }: { working: boolean }) {
             <span className="grid size-5 shrink-0 place-items-center text-primary">
               <WorkingSpinner spinning className="size-3.5" />
             </span>
-            <span className="shrink-0 tabular-nums">{elapsed}s</span>
+            <span className="shrink-0 font-mono tabular-nums">{elapsed}s</span>
             <span className="sr-only">ThothII is working</span>
           </div>
           {tailRows.length > 0 && (
-            <ol className="ml-7 flex flex-col gap-0.5 overflow-hidden rounded-md border border-border/50 bg-muted/40 px-3 py-2">
+            <ol className="ml-7 flex flex-col gap-0.5 overflow-hidden rounded-lg border border-border/60 bg-muted/40 px-3 py-2">
               {tailRows.map((line, i) => {
                 const isLast = i === tailRows.length - 1;
                 return (