feat(deps): Tailwind 3 → 4 + swap tailwindcss-animate for tw-animate-css

Ran the official @tailwindcss/upgrade tool:
- tailwind.config.ts → @theme directive in globals.css
- @tailwind base/components/utilities → @import 'tailwindcss'
- postcss.config switched from tailwindcss + autoprefixer to
  @tailwindcss/postcss (autoprefixer baked in)
- focus-visible:outline-none → focus-visible:outline-hidden (the v3
  utility was a footgun — outline still showed in forced-colors mode)

Reverted the migration tool's over-zealous variant="outline" →
variant="outline-solid" rename on CVA prop values; that rename was
meant for the Tailwind `outline:` utility, not our Button/Badge
component variants.

Swapped tailwindcss-animate (v3-style JS plugin) for tw-animate-css
(v4-native @import). Same utility surface (animate-spin, animate-in,
etc.), one fewer JS plugin in the bundle.

Fixed the upgrade tool's malformed dark variant
(@custom-variant dark (&:is(class *)) — `class` was being parsed as
a tag) to canonical &:where(.dark, .dark *).

Verified: tsc 0 errors, eslint 0 errors (16 pre-existing warnings),
vitest 1315/1315, next build clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/shared/branded-auth-shell.tsx

@@ -32,7 +32,7 @@ export function BrandedAuthShell({ children, branding }: BrandedAuthShellProps)
   const altText = branding?.appName || 'Port Nimara';
   // fixed inset-0 anchors the auth surface to the viewport directly —
   // iOS Safari ignores overflow-hidden on inner divs for body-level
-  // scrolling, so a regular `h-[100dvh] overflow-hidden` wrapper doesn't
+  // scrolling, so a regular `h-dvh overflow-hidden` wrapper doesn't
   // stop the rubber-band bounce. Pinning to the viewport via position
   // fixed does. The fixed-position shell then uses flex to center the
   // card within the visible area.