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/SteerInput.tsx

@@ -199,7 +199,7 @@ function FooterSelect({
       onChange={(e) => onChange(e.target.value)}
       {...rest}
       className={[
-        "max-w-[10rem] cursor-pointer truncate rounded-md border border-border bg-card px-1.5 py-0.5 text-[0.7rem] text-foreground/80 outline-none transition-colors hover:bg-muted focus:border-primary/40 focus:ring-2 focus:ring-ring/15",
+        "max-w-[10rem] cursor-pointer truncate rounded-lg border border-border bg-card px-1.5 py-0.5 text-[0.7rem] text-foreground/80 outline-none transition-colors hover:bg-muted focus:border-primary/40 focus:ring-2 focus:ring-ring/15",
         className,
       ].filter(Boolean).join(" ")}
     >