Adds Kubernetes sandbox provisioner support (#35)

* Adds Kubernetes sandbox provisioner support

* Improves Docker dev setup by standardizing host paths

Replaces hardcoded host paths with a configurable root directory,
making the development environment more portable and easier to use
across different machines. Automatically sets the root path if not
already defined, reducing manual setup steps.

backend/src/community/aio_sandbox/sandbox_info.py

@@ -0,0 +1,41 @@
+"""Sandbox metadata for cross-process discovery and state persistence."""
+
+from __future__ import annotations
+
+import time
+from dataclasses import dataclass, field
+
+
+@dataclass
+class SandboxInfo:
+    """Persisted sandbox metadata that enables cross-process discovery.
+
+    This dataclass holds all the information needed to reconnect to an
+    existing sandbox from a different process (e.g., gateway vs langgraph,
+    multiple workers, or across K8s pods with shared storage).
+    """
+
+    sandbox_id: str
+    sandbox_url: str  # e.g. http://localhost:8080 or http://k3s:30001
+    container_name: str | None = None  # Only for local container backend
+    container_id: str | None = None  # Only for local container backend
+    created_at: float = field(default_factory=time.time)
+
+    def to_dict(self) -> dict:
+        return {
+            "sandbox_id": self.sandbox_id,
+            "sandbox_url": self.sandbox_url,
+            "container_name": self.container_name,
+            "container_id": self.container_id,
+            "created_at": self.created_at,
+        }
+
+    @classmethod
+    def from_dict(cls, data: dict) -> SandboxInfo:
+        return cls(
+            sandbox_id=data["sandbox_id"],
+            sandbox_url=data.get("sandbox_url", data.get("base_url", "")),
+            container_name=data.get("container_name"),
+            container_id=data.get("container_id"),
+            created_at=data.get("created_at", time.time()),
+        )