refactor(ui): mobile-first pass on shared chrome + shadcn Field wrapper

- Field.tsx re-added composing shadcn Label (no built-in equivalent
  in this CLI generation).
- Bumped Input/Textarea to h-12/rounded-xl/px-4 (44px+ touch targets,
  matches the app's existing rounded, roomy input style).
- Card padding restored to the old flat p-5 sm:p-6 default so most
  call sites (`<Card>children</Card>`) don't need CardContent
  wrapping; CardHeader/Content/Footer still exported for the few
  structured cards.
- Swapped literal pink-500/gray-100 focus/border colors for
  text-primary / border-border / ring-ring tokens in Footer and
  CalendarButtons so brand color flows from the CSS vars.
- min-h-screen -> min-h-[100dvh] on full-bleed screens (home,
  create, not-found) so mobile browser chrome doesn't clip content.
- Responsive type scale (text-4xl sm:text-5xl md:text-6xl, etc.)
  instead of a single jump at md:, so headings don't overflow on
  narrow phones.
- Root layout now mounts <Toaster> and uses bg-background/
  text-foreground (background token matches the previous gray-50).

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

src/components/ui/textarea.tsx

@@ -9,7 +9,7 @@ const Textarea = React.forwardRef<
   return (
     <textarea
       className={cn(
-        "flex min-h-[60px] w-full rounded-md border border-input bg-transparent px-3 py-2 text-base shadow-sm placeholder:text-muted-foreground focus-visible:outline-none focus-visible:ring-1 focus-visible:ring-ring disabled:cursor-not-allowed disabled:opacity-50 md:text-sm",
+        "flex min-h-[80px] w-full rounded-xl border border-input bg-transparent px-4 py-3 text-base shadow-sm placeholder:text-muted-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring/40 focus-visible:border-ring disabled:cursor-not-allowed disabled:opacity-50",
         className
       )}
       ref={ref}