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>

package.json

@@ -104,9 +104,9 @@
     "sonner": "^2.0.7",
     "svgo": "^4.0.1",
     "tailwind-merge": "^3.6.0",
-    "tailwindcss-animate": "^1.0.7",
     "tesseract.js": "^7.0.0",
     "ts-pattern": "^5.9.0",
+    "tw-animate-css": "^1.4.0",
     "unpdf": "^1.6.2",
     "vaul": "^1.1.2",
     "web-vitals": "^5.2.0",
@@ -119,6 +119,7 @@
     "@hookform/devtools": "^4.4.0",
     "@next/bundle-analyzer": "^16.2.6",
     "@playwright/test": "^1.60.0",
+    "@tailwindcss/postcss": "^4.3.0",
     "@total-typescript/ts-reset": "^0.6.1",
     "@types/archiver": "^7.0.0",
     "@types/iso-3166-2": "^1.0.4",
@@ -129,7 +130,6 @@
     "@types/react-dom": "^19.2.3",
     "@vitejs/plugin-react": "^6.0.1",
     "@vitest/coverage-v8": "^4.1.6",
-    "autoprefixer": "^10.5.0",
     "dotenv": "^17.4.2",
     "drizzle-kit": "^0.31.10",
     "drizzle-zod": "^0.8.3",
@@ -142,7 +142,7 @@
     "postcss": "^8.5.14",
     "prettier": "^3.8.3",
     "react-grab": "^0.1.34",
-    "tailwindcss": "^3.4.19",
+    "tailwindcss": "^4.3.0",
     "tsx": "^4.21.0",
     "typescript": "^6.0.3",
     "vitest": "^4.1.6"