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/first-run.ts

@@ -27,7 +27,6 @@ import type {
   SetupCompletionResult,
   DetectedProject,
   RegisteredProject,
-  GlobalSettings,
 } from "./types.js";
 import type { CentralCore } from "./central-core.js";
 import { MigrationOrchestrator } from "./migration-orchestrator.js";