fix(delegate): give subagents independent iteration budgets (#3004)

Each subagent now gets its own IterationBudget instead of sharing the
parent's.  The per-subagent cap is controlled by delegation.max_iterations
in config.yaml (default 50).  Total iterations across parent + subagents
can exceed the parent's max_iterations, but the user retains control via
the config setting.

Previously, subagents shared the parent's budget, so three parallel
subagents configured for max_iterations=50 racing against a parent that
already used 60 of 90 would each only get ~10 iterations.

Inspired by PR #2928 (Bartok9) which identified the issue (#2873).

hermes_cli/config.py

@@ -317,6 +317,8 @@ DEFAULT_CONFIG = {
         "provider": "",    # e.g. "openrouter" (empty = inherit parent provider + credentials)
         "base_url": "",    # direct OpenAI-compatible endpoint for subagents
         "api_key": "",     # API key for delegation.base_url (falls back to OPENAI_API_KEY)
+        "max_iterations": 50,  # per-subagent iteration cap (each subagent gets its own budget,
+                               # independent of the parent's max_iterations)
     },
 
     # Ephemeral prefill messages file — JSON list of {role, content} dicts