### What problem does this PR solve?
This PR aligns `POST /api/v1/system/tokens` in Go with the Python
implementation.
### Type of change
- Keep the token creation flow under the system API route.
- Preserve the owner-tenant authorization check.
- Generate and persist API tokens consistently with the current Go
service flow.
- Return the created token payload in the standard API response format.
Co-authored-by: Jin Hai <haijin.chn@gmail.com>
### What problem does this PR solve?
This PR updates `SystemService.ListAPITokens` to lazily backfill missing
`beta` values for API tokens, matching the Python behavior of
`/api/v1/system/tokens`.
### Type of change
- When an API token has an empty `beta`, generate a new one.
- Persist the generated `beta` back to the `api_token` table.
- Keep the handler/routing unchanged.
- `GET /api/v1/system/tokens` now returns tokens with `beta` filled in
for older records that were missing it.
- This aligns Go behavior with the Python implementation.
### What problem does this PR solve?
Go cli
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
---------
Signed-off-by: Jin Hai <haijin.chn@gmail.com>
