chore(admin-web): add Prettier formatter with Svelte support

Add prettier + prettier-plugin-svelte as devDependencies with a
.prettierrc.json matching the existing code style (tabs, single quotes,
semicolons, trailing commas, 120 char width). Add .prettierignore for
build artifacts and lockfile. Wire up `npm run format` (write) and
`npm run format:check` (CI gate) scripts.

Prettier is chosen over Biome because its prettier-plugin-svelte correctly
preserves <script> block indentation per Svelte convention; Biome's
experimental Svelte formatter flattens script-block indentation to column 0,
producing inconsistent output.

hub/admin-web/package.json

@@ -9,7 +9,9 @@
 		"preview": "vite preview",
 		"prepare": "svelte-kit sync || echo ''",
 		"check": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json",
-		"check:watch": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json --watch"
+		"check:watch": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json --watch",
+		"format": "prettier --write .",
+		"format:check": "prettier --check ."
 	},
 	"devDependencies": {
 		"@skeletonlabs/skeleton": "^4.15.2",
@@ -20,6 +22,8 @@
 		"@sveltejs/vite-plugin-svelte": "^7.1.2",
 		"@tailwindcss/vite": "^4.3.2",
 		"bits-ui": "^2.18.1",
+		"prettier": "^3.9.5",
+		"prettier-plugin-svelte": "^4.1.1",
 		"svelte": "^5.56.1",
 		"svelte-check": "^4.6.0",
 		"tailwindcss": "^4.3.2",