chore: update @auth/sveltekit to v1.11.1 and remove direct @auth/core dependency

Updated authentication packages to latest versions for security fixes:
- @auth/sveltekit: 1.10.0 → 1.11.1 (includes nodemailer security fix)
- @auth/core: removed from devDependencies (transitively pulled as 0.41.1)

Changed imports to use @auth/sveltekit/providers instead of @auth/core/providers
and removed unused imports from hooks.server.ts.

package.json

@@ -18,7 +18,6 @@
 	},
 	"packageManager": "pnpm@9.0.0",
 	"devDependencies": {
-		"@auth/core": "^0.40.0",
 		"@playwright/test": "^1.56.1",
 		"@sveltejs/adapter-auto": "^6.1.0",
 		"@sveltejs/kit": "^2.37.0",
@@ -37,7 +36,7 @@
 		"vitest": "^4.0.10"
 	},
 	"dependencies": {
-		"@auth/sveltekit": "^1.10.0",
+		"@auth/sveltekit": "^1.11.1",
 		"@sveltejs/adapter-node": "^5.0.0",
 		"chart.js": "^4.5.0",
 		"cheerio": "1.0.0-rc.12",