feat: support sub agent mechanism

backend/src/subagents/builtins/__init__.py

@@ -0,0 +1,15 @@
+"""Built-in subagent configurations."""
+
+from .bash_agent import BASH_AGENT_CONFIG
+from .general_purpose import GENERAL_PURPOSE_CONFIG
+
+__all__ = [
+    "GENERAL_PURPOSE_CONFIG",
+    "BASH_AGENT_CONFIG",
+]
+
+# Registry of built-in subagents
+BUILTIN_SUBAGENTS = {
+    "general-purpose": GENERAL_PURPOSE_CONFIG,
+    "bash": BASH_AGENT_CONFIG,
+}