Runner create/list functionality

## Acceptance Criteria
- Modal: Name (required), Status (default Missing)
- POST /runners (owner = JWT uid) → list refresh user-scoped
- Table (Name, Status, Updated). Empty state if none.

## Test Notes
- Creating a runner shows immediately in My Runners
- User can only see their own runners
- Proper validation and error handling
- Empty state displays when no runners exist

No files or tests are named. Start by locating the existing runner UI and the POST /runners endpoint, then trace how JWT uid scoping and list refresh are handled. Done means creating a validated runner, showing it in the user-scoped table with Name, Status, and Updated fields, handling errors, and displaying the empty state.

Written by the indexing model from the issue text.