feat(FN-3636): add roadmap plugin with domain store and ordering logic

Merges the roadmap plugin scaffold (FN-3636): a new `plugins/fusion-plugin-roadmap` workspace with domain types (`roadmap-types.ts`), a store layer (`roadmap-store.ts`, `roadmap-ordering.ts`, `roadmap-handoff.ts`), and comprehensive test suites. Also lands graph position persistence for the dependen

Fusion-Task-Id: FN-3636

plugins/fusion-plugin-roadmap/package.json

@@ -0,0 +1,26 @@
+{
+  "name": "@fusion-plugin-examples/roadmap",
+  "version": "0.1.0",
+  "type": "module",
+  "description": "Roadmap domain and plugin manifest package for Fusion",
+  "private": true,
+  "exports": {
+    ".": {
+      "types": "./src/index.ts",
+      "import": "./dist/index.js"
+    }
+  },
+  "scripts": {
+    "build": "tsc",
+    "test": "vitest run --silent=passed-only --reporter=dot"
+  },
+  "dependencies": {
+    "@fusion/core": "workspace:*",
+    "@fusion/plugin-sdk": "workspace:*"
+  },
+  "devDependencies": {
+    "@types/node": "^25.5.2",
+    "typescript": "^5.7.0",
+    "vitest": "^3.2.4"
+  }
+}