refactor: extract NextActions into reusable workflow-surface models

Move wrapper-draft next_actions from handler-local dict helpers into
typed models in workflow_surface/next_actions.py. Adds NextActionTool
enum, NextActionPatchExample, and NextActions.from_wrapper_hints()
constructor. Replaces private _wrapper_draft_next_actions and
_wrapper_draft_patch_examples helpers. Adds can_continue as additive
advisory field. Keeps backward-compatible aliases in models.py.

tests/wf_mcp/server/test_config.py

@@ -116,6 +116,11 @@ def test_server_exposes_upstream_admin_and_workflow_tools() -> None:
             next_actions_schema = from_capability_output["properties"]["next_actions"]
             assert "recommended_next_tool" in next_actions_schema["properties"]
             assert "patch_examples" in next_actions_schema["properties"]
+            assert "can_continue" in next_actions_schema["properties"]
+            assert (
+                "Advisory"
+                in next_actions_schema["properties"]["can_continue"]["description"]
+            )
             assert (
                 "Advisory"
                 in next_actions_schema["properties"]["can_save_now"]["description"]