fix(delegation): honor api_mode + auto-detect anthropic_messages URLs (#26824)

Subagent delegation hardcoded api_mode='chat_completions' for any
delegation.base_url that didn't match three specific hostnames
(chatgpt.com, api.anthropic.com, api.kimi.com/coding), and never
read delegation.api_mode from config. Azure AI Foundry's
https://foundry.services.ai.azure.com/anthropic endpoint fell through
and got chat_completions, causing 404s on every delegate_task call.

The main agent already handles this correctly via the shared
_detect_api_mode_for_url() helper (anything ending in /anthropic →
anthropic_messages); delegation reimplemented its own narrower check.

Reuse the shared detector and honor an explicit delegation.api_mode
when set so users can also force the transport on non-standard
endpoints the URL heuristic can't classify.

Fixes #10213.

Co-authored-by: HiddenPuppy <HiddenPuppy@users.noreply.github.com>

hermes_cli/config.py

@@ -1146,6 +1146,10 @@ 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)
+        "api_mode": "",    # wire protocol for delegation.base_url: "chat_completions",
+                           # "codex_responses", or "anthropic_messages". Empty = auto-detect
+                           # from URL (e.g. /anthropic suffix → anthropic_messages). Set this
+                           # explicitly for non-standard endpoints the heuristic can't detect.
         # When delegate_task narrows child toolsets explicitly, preserve any
         # MCP toolsets the parent already has enabled. On by default so
         # narrowing (e.g. toolsets=["web","browser"]) expresses "I want these