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/routine-store.ts

@@ -10,7 +10,7 @@
 import { EventEmitter } from "node:events";
 import { randomUUID } from "node:crypto";
 import { CronExpressionParser } from "cron-parser";
-import { Database, toJson, fromJson } from "./db.js";
+import { Database, fromJson } from "./db.js";
 import {
   isCronTrigger,
   type Routine,