feat(FN-4468): add workflow step gateMode advisory gating

Adds an "advisory" `gateMode` option for workflow steps: steps in advisory mode log findings but no longer block merge completion, while steps that must block can still be configured as blocking. The change covers the workflow step types and schema, executor gating logic, dashboard UI in WorkflowSte

Fusion-Task-Id: FN-4468

plugins/fusion-plugin-roadmap/src/store/__tests__/roadmap-store.test.ts

@@ -743,8 +743,8 @@ describe("RoadmapStore", () => {
   });
 
   describe("schema version", () => {
-    it("schema version is 75 after init", () => {
-      expect(db.getSchemaVersion()).toBe(75);
+    it("schema version is 76 after init", () => {
+      expect(db.getSchemaVersion()).toBe(76);
     });
   });