Adds a per-agent hyperhive.availableModels list option (default
[ haiku sonnet opus ]) rendered into the HIVE_AVAILABLE_MODELS env var
(comma-separated) so the per-agent web UI model quick-picker lists
exactly the configured models instead of a hardcoded set. Operators set
a shared default hive-wide or narrow it per-agent.
An assertion guards that hyperhive.model is present in the list so the
picker can always offer the model the agent is actually running.
e5da9654f1