refactor(workflow): cleanup engine re-exports, final verification (Phase 4)

- Remove all re-exports from @uncaged/workflow -> @uncaged/workflow-runtime
- Fix cli-workflow imports to use @uncaged/workflow-runtime for types
- Update bundle-validator to allow @uncaged/workflow-runtime imports
- Update init templates to reference @uncaged/workflow-runtime
- 378 tests passing, build + check clean

Refs #121, relates #125

package.json

@@ -5,6 +5,7 @@
     "packages/*"
   ],
   "scripts": {
+    "build": "bunx tsc --build",
     "check": "bunx tsc --build && biome check .",
     "typecheck": "bunx tsc --build",
     "format": "biome format --write .",