Upgrade dependencies to latest stable versions, migrate Tailwind CSS v3 to v4

Bumped React, Supabase JS, and type packages to latest patch/minor releases.
Migrated the Tailwind pipeline from the v3 JS-config format to v4's CSS-first
@theme setup (@tailwindcss/postcss, @import "tailwindcss" in globals.css),
removing tailwind.config.ts and autoprefixer since v4 handles both natively.
All existing color/radius/font tokens were ported 1:1 so no component classes
needed to change. TypeScript and ESLint were bumped and tested against their
true latest majors (7.x and 10.x) but both broke the build/lint pipeline, so
they're pinned to the latest working minor instead (TypeScript 5.9.3, ESLint
9.39.5).

postcss.config.js

@@ -1,6 +1,5 @@
 module.exports = {
   plugins: {
-    tailwindcss: {},
-    autoprefixer: {},
+    "@tailwindcss/postcss": {},
   },
 };