🔧 chore: Enforce isolatedDeclarations in data-schemas tsconfig (#13593)

Enable `isolatedDeclarations` (and `declaration`) in
packages/data-schemas/tsconfig.json so any exported declaration missing
an explicit type annotation is flagged directly in editors and the CI
typecheck, instead of only surfacing during the tsdown/oxc dts emit at
build time.

The package is already fully annotated, so this is a zero-error,
enforcement-only change that keeps data-schemas eligible for the fast
oxc-based declaration emit going forward.

packages/data-schemas/tsconfig.json

@@ -3,7 +3,8 @@
     "target": "ES2019",
     "module": "ESNext",
     "moduleResolution": "bundler",
-    "declaration": false,
+    "declaration": true,
+    "isolatedDeclarations": true,
     "noEmit": true,
     "strict": true,
     "esModuleInterop": true,