refactor(a2a): tools._load_config reads config through load_config_readonly

The 6-line try/except copy of "load_config() or {}" (also in doctor_live and
kanban_decompose, hermes_cli lane) took a full deepcopy per tool call for a
dict that is only read. load_config_readonly already degrades to the
last-known-good / defaults on a broken file, so the outer except was
defense-in-depth around a path that does not raise. Behavior change: none.
Tests already patch tools._load_config by name and continue to pass.

plugins/platforms/a2a/tools.py

@@ -24,11 +24,9 @@ _ORCHESTRATE_MAX_WORKERS = 6  # max parallel peers for fan-out
 
 
 def _load_config() -> dict:
-    try:
-        from hermes_cli.config import load_config
-        return load_config() or {}
-    except Exception:
-        return {}
+    """Read-only view of config.yaml; peers are only read, never mutated (cache-safe)."""
+    from hermes_cli.config import load_config_readonly
+    return load_config_readonly() or {}
 
 
 def _configured_peers() -> dict: