[Nice-to-Have] Recent Workspaces List

## Priority: Nice-to-Have (Can Ship Without)

Show a list of recently opened workspaces on the welcome screen so users can quickly switch between projects.

### Scope

- Persist a list of recently opened workspace paths (e.g., via `tauri-plugin-store`).
- Display the list on the welcome/landing screen.
- Allow clicking an entry to open that workspace directly.

_Source: changelogs/cinder-v0.2.md_