Route all app commands through a single RPC envelope (#542)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Cargo.lock

@@ -11034,6 +11034,7 @@ dependencies = [
  "yaak-mac-window",
  "yaak-models",
  "yaak-plugins",
+ "yaak-rpc",
  "yaak-sse",
  "yaak-sync",
  "yaak-system-appearance",
@@ -11201,6 +11202,7 @@ dependencies = [
  "tokio-stream",
  "tonic",
  "tonic-reflection",
+ "ts-rs",
  "uuid",
  "yaak-common",
  "yaak-tls",