feat(execute): create @uncaged/workflow-execute + CLI migration

Phase 7: Engine + extract + workflow-as-agent merged into execute package.
All CLI imports migrated from @uncaged/workflow to specific packages.
105 CLI tests pass, 0 failures.

Changes:
- New @uncaged/workflow-execute package (engine/, extract/, workflow-as-agent)
- CLI src/ and __tests__/ rewritten to import from split packages
- bundle-validator updated to allow @uncaged/workflow-cas imports
- ensure-uncaged-workflow-symlink creates symlinks for all new packages

Ref: #143, closes #150

packages/cli-workflow/package.json

@@ -6,8 +6,12 @@
     "uncaged-workflow": "src/cli.ts"
   },
   "dependencies": {
+    "@uncaged/workflow-protocol": "workspace:*",
+    "@uncaged/workflow-util": "workspace:*",
+    "@uncaged/workflow-cas": "workspace:*",
+    "@uncaged/workflow-execute": "workspace:*",
+    "@uncaged/workflow-register": "workspace:*",
     "@uncaged/workflow-runtime": "workspace:*",
-    "@uncaged/workflow": "workspace:*",
     "hono": "^4.12.18",
     "yaml": "^2.8.4"
   },