Three changes to replace raw UUIDs/hex-ids with stable user-facing labels:
1. Turn label: Add turn_counter to App, display "Turn N" instead of the
raw runtime_turn_id UUID prefix. Full UUID preserved in hover text.
2. Agent labels: Add agent_counter + agent_label_map to App. Populated
on AgentSpawned; sidebar rows use "Agent 1", "Agent 2" etc. instead
of agent_<hex>. Nicknames and user-assigned names still take priority.
3. Step counter: Add format_step_counter() helper. When max_steps is
u32::MAX (the unbounded sentinel), renders "step 16" instead of the
meaningless "step 16/4294967295". Concrete step budgets still show
the denominator.
Hunter Bown
ec0789daf4