Remove the old leaf declaration path

Delete the deprecated Leaf derive path, migrate the remaining tests and example to leaf!, and add direct coverage for endpoint-only, TUI-only, and shared-host leaf declarations.

src/lib.rs

@@ -26,6 +26,6 @@ pub use unshell_protocol as protocol;
 /// Re-export the leaf library crate behind the historical `unshell::leaves` path
 pub use unshell_leaves as leaves;
 
-pub use unshell_macros::{Leaf, Procedure, leaf, procedures};
+pub use unshell_macros::{Procedure, leaf, procedures};
 
 // pub use ush_obfuscate as obfuscate;