Add compile-time leaf declarations

Introduce a function-like leaf declaration macro, bind endpoint and TUI hosts to shared generated metadata, and move remote shell endpoint construction out of the leaf module into the examples and runtime assembly code.

examples/protocol/remote_shell_single_endpoint.rs

@@ -16,10 +16,7 @@ fn main() -> Result<(), Box<dyn Error>> {
         agent_path(),
         Some(Vec::new()),
         Vec::new(),
-        vec![unshell::protocol::tree::LeafSpec {
-            name: remote_shell::endpoint::RemoteShellEndpoint::protocol_leaf_name(),
-            procedures: vec![remote_shell::endpoint::ProcedureOpen::protocol_procedure_id()],
-        }],
+        vec![remote_shell::endpoint::RemoteShellEndpoint::protocol_leaf_spec()],
     );
 
     let hook_id = endpoint.allocate_hook_id();