Implement Runner Create + List (User-Scoped)

## Overview
Implement runner creation and listing functionality scoped to the current user.

## Acceptance Criteria
- [ ] Modal RunnerForm:
- Fields: Name (required), Status (default Missing), DOB (optional), Notes
- Submit → POST /api/v1/runners (owner = JWT uid)
- [ ] RunnerList:
- Columns: Name, Status, Updated, Actions (Edit/Delete disabled for now)
- Empty state if none
- Pagination params supported (page, pageSize)
- [ ] Creating a runner shows it in My Runners immediately
- [ ] List is scoped to the current user

## Test Notes
- Test runner creation with valid data
- Test runner list displays created runners
- Test empty state when no runners exist
- Test pagination if many runners exist

## Implementation Notes
- Use existing API endpoints for runner operations
- Implement proper form validation
- Add loading states during operations
- Ensure proper error handling and user feedback

Start by locating the existing runner API endpoints and the React entry points named RunnerForm and RunnerList. Exercise POST /api/v1/runners and the list with page/pageSize for valid, empty, and multi-runner cases; done means creation appears in My Runners, results are scoped to the JWT uid, validation/loading/error feedback works, and edit/delete remain disabled.

Written by the indexing model from the issue text.