Add independent `share_memory` config flag to control memory and
knowledge graph sharing separately from workspace folder isolation.
- Add ShareMemory field to WorkspaceSharingConfig
- Decouple WithSharedMemory(ctx) from shouldShareWorkspace() in loop.go
- Add shouldShareMemory() helper independent of workspace sharing
- Fix KG Traverse CTE to scope user_id in recursive step (pre-existing bug)
- Add memory toggle UI with violet styling in workspace sharing section
- Add i18n translations (en/vi/zh) for new memory sharing controls
- Add unit tests for shouldShareMemory() independence