Initial import of Shirobana bot backend

Include utility modules, shared channels, prompts, read-only skills, wardrobe memory and regression tests. Externalize legacy credentials and exclude private runtime state.

bot-utility/agent/runtime.py

@@ -0,0 +1,19 @@
+"""Compatibility import surface for the agent notification layer."""
+
+from .artifacts import ArtifactError, ArtifactStore
+from .capture import CaptureChannel
+from .executor import ToolExecutor
+from .models import ToolContext, ToolResult
+from .modes import ModeStore, get_mode, set_mode
+
+__all__ = [
+    "ArtifactError",
+    "ArtifactStore",
+    "CaptureChannel",
+    "ModeStore",
+    "ToolContext",
+    "ToolExecutor",
+    "ToolResult",
+    "get_mode",
+    "set_mode",
+]