fix(hub): preserve permission mode on resume

[webwww123]

Summary

Preserve the previous permission mode when resuming an archived session.

What changed

• persist the last known permission mode in session metadata
• restore that mode when rebuilding session state from the store
• automatically reapply the saved permission mode during session resume
• preserve the saved mode when old/new sessions are merged after resume
• add hub tests covering persistence and resume-time reapplication

Why

Without this, sessions resumed from archive fall back to default, even if the user was previously using a more permissive mode like YOLO. That forces users to stop the agent, switch modes again, and wastes tokens.

Closes #281

Validation

docker run --rm -v "/root/sandbox/hapi-pr:/workspace:ro" oven/bun:1 sh -lc "cp -a /workspace /tmp/hapi-pr && cd /tmp/hapi-pr && bun install && cd hub && bun test src/sync/permissionModePersistence.test.ts && cd /tmp/hapi-pr && bun run typecheck"