fix: make MemOS startup recovery non-blocking

[leavrcn]

Summary

• Make MemOS startup recovery for stale open / dirty closed episodes non-blocking during MemoryCore.init().
• Schedule startup recovery work in the background so session.open can return promptly even when recovery triggers slow reward/LLM work.
• Add a focused regression test that locks the init-time non-blocking contract.

Why

Hermes adapter opens a JSON-RPC bridge session during startup. If init() synchronously waits for stale/dirty episode recovery, recovery can call slow scoring paths and prevent session.open from responding before the adapter timeout. The host then kills/restarts bridge processes and can enter a reconnect storm.

Test plan

• npm --prefix apps/memos-local-plugin test -- tests/unit/startup-recovery.test.ts
• cd apps/memos-local-plugin && npm run lint