feat(FN-3638): extract roadmap domain into plugin and define plugin route s

This merge restructures the roadmap plugin by removing its duplicated domain logic (roadmap store, ordering, handoff, and types — ~3,000 lines deleted) and completing the plugin SDK scaffold with proper route status/body contracts and type exports. It also introduces eval settings infrastructure wit

Fusion-Task-Id: FN-3638

packages/core/src/index.ts

@@ -150,6 +150,8 @@ export type {
   PluginToolResult,
   PluginRouteDefinition,
   PluginRouteMethod,
+  PluginRouteResponse,
+  PluginRouteResult,
   PluginUiSurface,
   PluginUiSlotDefinition,
   PluginUiContributionSurface,

packages/core/src/plugin-types.ts

@@ -196,11 +196,18 @@ export type PluginRouteMethod = "GET" | "POST" | "PUT" | "DELETE";
 /**
  * Custom dashboard API route definition.
  */
+export interface PluginRouteResponse {
+  status: number;
+  body?: unknown;
+}
+
+export type PluginRouteResult = unknown | PluginRouteResponse;
+
 export interface PluginRouteDefinition {
   method: PluginRouteMethod;
   /** Relative path under /api/plugins/:pluginId/ */
   path: string;
-  handler: (req: unknown, ctx: PluginContext) => Promise<unknown>;
+  handler: (req: unknown, ctx: PluginContext) => Promise<PluginRouteResult>;
   description?: string;
 }