feat(protocol): create @uncaged/workflow-protocol package

Extract all cross-package type definitions and constructor functions
into a dedicated protocol layer. This is the foundation for the
seven-package split (RFC #143).

Contains:
- Result<T,E>, ok(), err()
- START, END constants
- CasStore, WorkflowFn, RoleOutput, WorkflowCompletion
- WorkflowDescriptor, WorkflowRoleDescriptor
- ProviderConfig, WorkflowConfig, ResolvedModel (fixes config↔registry cycle)
- RoleDefinition, Moderator, WorkflowDefinition
- AgentFn, ExtractFn, and all thread context types

Ref: #143, closes #144

packages/workflow-protocol/tsconfig.json

@@ -0,0 +1,8 @@
+{
+  "extends": "../../tsconfig.json",
+  "compilerOptions": {
+    "rootDir": "src",
+    "outDir": "dist"
+  },
+  "include": ["src"]
+}