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/worker.py

@@ -1282,7 +1282,7 @@ def infer_foreground_frames(
 
 def remove_background(args, model_cache=None, cancel_check=None):
     total_started = time.perf_counter()
-    write_status(args.status, 0.02, "Starting BEN2 Runtime")
+    write_status(args.status, 0.02, "Starting Backend Environment")
     check_cancelled(cancel_check)
 
     if model_cache is None:
@@ -1501,7 +1501,7 @@ def flatten_exported_paths(
 
 
 def reconstruct(args, model_cache=None, cancel_check=None):
-    write_status(args.status, 0.02, "Starting AI runtime")
+    write_status(args.status, 0.02, "Starting Backend Environment")
     check_cancelled(cancel_check)
 
     if model_cache is None: