Position the spawn modal directly under the 'New Agent' button without a
blur overlay. Uses click-outside dismissal and absolute positioning.
Reduces visual disruption for quick agent spawning.
- Add empty-state message in SpawnModal when no projects found
- Spawn button stays disabled when projects list is empty
- Server already handled OSError/missing dir gracefully (returns [])
- Add tests: missing directory, only-hidden-dirs, empty API responses
Closes: bd-3c7