- Add src/timmy/workspace.py: WorkspaceMonitor tracks correspondence.md
line count and inbox file list via data/workspace_state.json
- Wire workspace checks into _gather_system_snapshot() so Timmy sees
new workspace activity in his thinking context
- Add 'workspace' seed type for workspace-triggered reflections
- Add _check_workspace() post-hook to mark items as seen after processing
- 16 tests covering detection, mark_seen, persistence, edge cases
