OpenAPI: total_flux must be non-negative

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HVeDQsU5a8AJUdJPgWevAK

broker/jfjoch_api.yaml

@@ -480,6 +480,7 @@ components:
         total_flux:
           type: number
           format: float
+          minimum: 0.0
           description: |
             /entry/beam/total_flux in NXmx
             Flux incident on beam plane in photons per second. In other words this is the flux integrated over area. [photons/s]