Refactor AI Host to Backend Service and update related components

- Renamed references from "AI Host" to "Backend Service" throughout the codebase for consistency.
- Updated the registration and unregistration of context menus to include the Outliner.
- Changed the job protocol versioning and related constants for clarity.
- Modified the runtime installation messages and error handling to reflect the new terminology.
- Adjusted the user interface labels and messages in panels and operators to align with the new Backend Service terminology.
- Updated tests to ensure they reflect the changes in naming and functionality.
- Changed default value for background depth in geometry nodes asset to -1.0 for better handling of depth planes.

src/snapform/image_depth.py

@@ -1823,7 +1823,7 @@ class ConvertImageToDepthPlane(bpy.types.Operator):
             available_models = image_depth_model_items(self, context)
             if not available_models:
                 estimate_box.label(text="No DA3 models installed", icon="ERROR")
-                estimate_box.label(text="Download one in Host > Models")
+                estimate_box.label(text="Download one in AI Backend > Models")
             else:
                 estimate_box.prop(self, "snapform_model")
                 estimate_box.prop(self, "snapform_use_ray_pose")
@@ -1917,8 +1917,18 @@ class SnapFormImageMenu(bpy.types.Menu):
     bl_label = "SnapForm"
 
     def draw(self, _context):
+        from .runtime import runtime_ready
+
         layout = self.layout
         layout.operator_context = "INVOKE_DEFAULT"
+        if not runtime_ready():
+            operator = layout.operator(
+                "snapform.run_job",
+                text="Install Backend",
+                icon="IMPORT",
+            )
+            operator.job_type = "INSTALL_RUNTIME"
+            return
         layout.operator(
             "snapform.convert_image_to_depth_plane",
             text="Convert to Depth Plane",