refactor(workflow): scaffold @uncaged/workflow, move types from core

- Create packages/workflow/ with types.ts (from core/workflow.ts) and config.ts
- Core re-exports workflow types from @uncaged/workflow
- Delete packages/core/src/workflow.ts

Phase 1+2 of #320, Testing: #321

pnpm-lock.yaml

@@ -86,6 +86,9 @@ importers:
 
   packages/core:
     dependencies:
+      '@uncaged/workflow':
+        specifier: workspace:*
+        version: link:../workflow
       yaml:
         specifier: ^2.8.3
         version: 2.8.3
@@ -215,6 +218,15 @@ importers:
         specifier: ^4.1.5
         version: 4.1.5(@types/node@22.19.17)(vite@8.0.9(@types/node@22.19.17)(esbuild@0.27.7)(yaml@2.8.3))
 
+  packages/workflow:
+    devDependencies:
+      '@rslib/core':
+        specifier: ^0.21.3
+        version: 0.21.3(typescript@5.9.3)
+      '@types/node':
+        specifier: ^22.0.0
+        version: 22.19.17
+
   packages/workflow-meta:
     dependencies:
       '@uncaged/nerve-core':