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/NewSessionDialog.tsx

@@ -63,7 +63,7 @@ export function NewSessionDialog({ onCreated }: Props) {
               value={question}
               onChange={(e) => setQuestion(e.target.value)}
               rows={3}
-              className="w-full resize-none rounded-lg border border-input bg-card px-3 py-2 text-sm outline-none transition-colors placeholder:text-muted-foreground focus:border-primary/50 focus:ring-3 focus:ring-ring/15"
+              className="w-full resize-none rounded-lg border border-input bg-card px-3 py-2 text-sm shadow-xs outline-none transition-[border-color,box-shadow] placeholder:text-muted-foreground focus:border-primary/50 focus:ring-3 focus:ring-ring/15"
               placeholder="Enter your question…"
             />
           </div>