refactor(core): remove unused imports, helpers, and dead migration constant

Drops orphaned imports and the never-referenced V4 migration SQL constant
(V4 was inlined into runMigrations). Also drops the unused TypedEventEmitter
helper type and unused destructured values from stores.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/core/src/roadmap-store.ts

@@ -13,7 +13,6 @@
 
 import { EventEmitter } from "node:events";
 import type { Database } from "./db.js";
-import { toJsonNullable } from "./db.js";
 import type {
   Roadmap,
   RoadmapMilestone,
@@ -35,9 +34,7 @@ import type {
   RoadmapFeatureSourceRef,
 } from "./roadmap-types.js";
 import {
-  normalizeRoadmapMilestoneOrder,
   applyRoadmapMilestoneReorder,
-  normalizeRoadmapFeatureOrder,
   applyRoadmapFeatureReorder,
   moveRoadmapFeature,
 } from "./roadmap-ordering.js";
@@ -394,8 +391,6 @@ export class RoadmapStore extends EventEmitter<RoadmapStoreEvents> {
       throw new Error(`Milestone ${id} not found`);
     }
 
-    const roadmapId = milestone.roadmapId;
-
     // SQLite FK cascade will handle features
     this.db.prepare("DELETE FROM roadmap_milestones WHERE id = ?").run(id);
     this.db.bumpLastModified();