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-lock.json

@@ -16,6 +16,8 @@
 				"@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",
@@ -2196,6 +2198,37 @@
 				"node": "^10 || ^12 || >=14"
 			}
 		},
+		"node_modules/prettier": {
+			"version": "3.9.5",
+			"resolved": "https://registry.npmmirror.com/prettier/-/prettier-3.9.5.tgz",
+			"integrity": "sha512-/FVl766LpUfB5vXgCYOYa0MeV/441Ia99AeICQIQFTY/Nw0roZwULcXpku5i1/m5kt/baz+s4Zogspd839HSMg==",
+			"dev": true,
+			"license": "MIT",
+			"peer": true,
+			"bin": {
+				"prettier": "bin/prettier.cjs"
+			},
+			"engines": {
+				"node": ">=14"
+			},
+			"funding": {
+				"url": "https://github.com/prettier/prettier?sponsor=1"
+			}
+		},
+		"node_modules/prettier-plugin-svelte": {
+			"version": "4.1.1",
+			"resolved": "https://registry.npmmirror.com/prettier-plugin-svelte/-/prettier-plugin-svelte-4.1.1.tgz",
+			"integrity": "sha512-wXvbXMjSvb4C9ENWTHXyd+ihakKCsJ6rJhLP6/8HFNj4GkZr48jqL9PoKsl2sk7SyCZRTnJ7O2TTowUpOxP/KA==",
+			"dev": true,
+			"license": "MIT",
+			"engines": {
+				"node": ">=20"
+			},
+			"peerDependencies": {
+				"prettier": "^3.0.0",
+				"svelte": "^5.0.0"
+			}
+		},
 		"node_modules/proxy-compare": {
 			"version": "3.0.1",
 			"resolved": "https://registry.npmmirror.com/proxy-compare/-/proxy-compare-3.0.1.tgz",