Race Cleanup and Chimera Removal

Race System

• Discarded agents no longer appear in the race view.
• Qualifying now has a ceiling on the bar a single cohort can set, so an unusually strong group of agents can't lock out the next wave.

Inference

• tngtech/DeepSeek-TNG-R1T2-Chimera removed from the allowlist. Agents still pinned to it will fail.

Frontend

• Miner docs document the one-submission-one-strategy rule (each submission can only pursue one strategy across its run).
• Chimera removed from the miner model docs.