feat(FN-3159): move roadmap ownership from core to fusion-plugin-roadmap pl

Moves roadmap ownership from `@fusion/core` to `fusion-plugin-roadmap`, deleting ~1,800 lines of roadmap store, types, ordering, and handoff logic from core and replacing it with ~760 lines of new route handlers in the plugin. The dashboard's roadmap routes and suggestions modules are substantially

Fusion-Task-Id: FN-3159

plugins/fusion-plugin-roadmap/src/roadmap-suggestions.ts

@@ -1 +1,15 @@
-export {};
+export {
+  FEATURE_SUGGESTION_SYSTEM_PROMPT,
+  MILESTONE_SUGGESTION_SYSTEM_PROMPT,
+  ParseError,
+  ServiceUnavailableError,
+  SUGGESTION_TIMEOUT_MS,
+  ValidationError,
+  __resetSuggestionState,
+  __setCreateAiSessionFactory,
+  __setCreateFnAgent,
+  generateFeatureSuggestions,
+  generateMilestoneSuggestions,
+  validateFeatureSuggestionInput,
+  validateSuggestionInput,
+} from "./routes/roadmap-suggestions.js";