feat(FN-3162): add plugin-owned roadmap schema hook and store bootstrap

The merge introduces a plugin-owned roadmap schema system (FN-3162), allowing plugins to define their own schema initialization hook, with tests bootstrapped in the roadmap store and documentation added to the plugin authoring guide. The parallel FN-3281 work delivers review revisions, updates the l

Fusion-Task-Id: FN-3162

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

@@ -1,6 +1,7 @@
 import { describe, it, expect, beforeEach, afterEach, vi } from "vitest";
 import { Database, createDatabase } from "@fusion/core";
 import { RoadmapStore } from "../roadmap-store.js";
+import { ensureRoadmapSchema } from "../../roadmap-schema.js";
 import type {
   RoadmapCreateInput,
   RoadmapUpdateInput,
@@ -33,6 +34,7 @@ describe("RoadmapStore", () => {
     // Database instances explicitly (search for `persistDb`).
     db = new Database(join(tmpDir, ".fusion"), { inMemory: true });
     db.init();
+    ensureRoadmapSchema(db);
     store = new RoadmapStore(db);
   });