fix(config): add missing eslint devDependency

The package declared an eslint lint script but eslint was not in
devDependencies, causing the pre-push hook to fail.

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

packages/config/package.json

@@ -27,6 +27,7 @@
     "@mosaic/storage": "workspace:^"
   },
   "devDependencies": {
+    "eslint": "^9.0.0",
     "typescript": "^5.8.0",
     "vitest": "^2.0.0"
   },

pnpm-lock.yaml

@@ -369,6 +369,9 @@ importers:
         specifier: workspace:^
         version: link:../storage
     devDependencies:
+      eslint:
+        specifier: ^9.0.0
+        version: 9.39.4(jiti@2.6.1)
       typescript:
         specifier: ^5.8.0
         version: 5.9.3