feat(delegation): bump default child_timeout_seconds to 600s (#14809)

The 300s default was too tight for high-reasoning models on non-trivial
delegated tasks — e.g. gpt-5.5 xhigh reviewing 12 files would burn >5min
on reasoning tokens before issuing its first tool call, tripping the
hard wall-clock timeout with 0 api_calls logged.

- tools/delegate_tool.py: DEFAULT_CHILD_TIMEOUT 300 -> 600
- hermes_cli/config.py: surface delegation.child_timeout_seconds in
  DEFAULT_CONFIG so it's discoverable (previously the key was read by
  _get_child_timeout() but absent from the default config schema)

Users can still override via config.yaml delegation.child_timeout_seconds
or DELEGATION_CHILD_TIMEOUT_SECONDS env var (floor 30s, no ceiling).

hermes_cli/config.py

@@ -739,6 +739,10 @@ DEFAULT_CONFIG = {
         "inherit_mcp_toolsets": True,
         "max_iterations": 50,  # per-subagent iteration cap (each subagent gets its own budget,
                                # independent of the parent's max_iterations)
+        "child_timeout_seconds": 600,  # wall-clock timeout for each child agent (floor 30s,
+                                       # no ceiling). High-reasoning models on large tasks
+                                       # (e.g. gpt-5.5 xhigh, opus-4.6) need generous budgets;
+                                       # raise if children time out before producing output.
         "reasoning_effort": "",  # reasoning effort for subagents: "xhigh", "high", "medium",
                                  # "low", "minimal", "none" (empty = inherit parent's level)
         "max_concurrent_children": 3,  # max parallel children per batch; floor of 1 enforced, no ceiling