* fix(app): preserve New Workspace prompts across target changes
The New Workspace draft was keyed by the selected host and project, so changing either target replaced the visible prompt with another draft scope. Treat the screen as one persistent draft surface and migrate the newest active legacy draft.
* test(app): express draft persistence as user actions
* fix(app): clear stale picker PR context
* fix(app): persist picker attachment ownership
* fix(app): keep workspace target context safe
Replace inline data-URL image handling with a persistent attachment storage service, add draft lifecycle states (active/abandoned/sent) with generation tracking, and update fetchAgent to return project placement alongside agent snapshots.
