Set up Tailwind CSS v4 + shadcn/ui + TypeScript foundation

Install Tailwind v4 with @tailwindcss/vite plugin, TypeScript, and
shadcn/ui (button + sheet components). Convert shared layout files
(App, AdminNavbar, AuthContext, ProtectedRoute, useSocket, api) from
JSX/JS to TSX/TS with type annotations. Rebuild AdminNavbar using
shadcn Button and Sheet components with Tailwind classes, replacing
custom CSS. Page components remain as JSX for incremental migration.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/frontend/tsconfig.json

@@ -0,0 +1,10 @@
+{
+	"compilerOptions": {
+		"baseUrl": ".",
+		"paths": {
+			"@/*": ["./src/*"]
+		}
+	},
+	"files": [],
+	"references": [{ "path": "./tsconfig.app.json" }]
+}