feat(Common/IPC): Add ExtHostDebug proxy target

Added `ExtHostDebug` variant to the `ProxyTarget` enum in the Common crate's IPC DTO module. This change extends the RPC proxy targets to support the debug extension host capability, which is a prerequisite for implementing the debug API in the `Cocoon` sidecar and `Mountain` backend.

The `ProxyTarget` enum is used by the `Track` dispatcher in `Mountain` to route RPC calls and by `Cocoon` to register its capabilities. This addition enables the debug extension host to be integrated into the existing RPC system (`Vine` gRPC layer), supporting the debugging workflow implementation. The `GetTargetPrefix()` method will now generate appropriate RPC method prefixes (e.g., `ExtHostDebug$MethodName`) for debug-related operations.

This aligns with Land's architecture where Common defines the abstract IPC contracts that both Mountain (Rust backend) and Cocoon (TypeScript extension host) implement, enabling type-safe communication through the Vine IPC layer.

Author: NikolaRHristov

Source/IPC/DTO/ProxyTarget.rs

@@ -115,11 +115,13 @@ pub enum ProxyTarget {
 	ExtHostSourceControlManagement,
 
 	ExtHostTesting,
+
+	ExtHostDebug,
 }
 
 impl ProxyTarget {
 	/// Returns a string prefix representing the target, used in constructing
-	/// fully qualified RPC method names (e.g.,
+	/// fully qualified RPC method names (e.g.
 	/// `MainThreadCommands$ExecuteCommand`).
 	pub fn GetTargetPrefix(&self) -> String { format!("{:?}", self) }
 }