refactor: split types.ts into domain modules (phase 4, step 1)

Split 1,443-line types.ts into 14 focused domain files under src/types/:
common.ts, session.ts, task.ts, app-state.ts, respawn.ts, ralph.ts,
api.ts, lifecycle.ts, run-summary.ts, tools.ts, teams.ts, push.ts,
plan.ts, and index.ts barrel.

Moved PlanItem interface from plan-orchestrator.ts into types/plan.ts
to break circular dependency. Original types.ts replaced with barrel
re-export — zero changes to 36 import sites.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/types/push.ts

@@ -0,0 +1,21 @@
+/**
+ * @fileoverview Web Push notification type definitions
+ */
+
+/** A registered push subscription */
+export interface PushSubscriptionRecord {
+  id: string;
+  endpoint: string;
+  keys: { p256dh: string; auth: string };
+  userAgent: string;
+  createdAt: number;
+  lastUsedAt: number;
+  pushPreferences: Record<string, boolean>;
+}
+
+/** VAPID key pair for Web Push */
+export interface VapidKeys {
+  publicKey: string;
+  privateKey: string;
+  generatedAt: number;
+}