feat: project memory

[embire2]

Summary

• add a Project Memory dialog (per‑chat notes) and persist memory per chat
• include project memory in /api/chat requests and inject it as a fenced user message to avoid system‑prompt override
• prevent settings overwrite on chat switch via a save‑skip guard
• clean up project memory entries when chats are deleted or imports reset

Testing

• pnpm run typecheck
• pnpm run lint
• e2e: Playwright smoke (set Project Memory, send chat, assert /api/chat payload includes projectMemory)