Feat: add hidden mode and new documentation

src/app/clipboard.rs

@@ -1,3 +1,5 @@
+//! Clipboard operations on steps, patterns, and banks.
+
 use crate::model;
 use crate::services::clipboard;
 use crate::state::FlashKind;
@@ -273,6 +275,7 @@ impl App {
         }
     }
 
+    /// Convert linked steps into independent copies.
     pub fn harden_steps(&mut self) {
         let (bank, pattern) = self.current_bank_pattern();
         let indices = self.selected_steps();
@@ -342,6 +345,7 @@ impl App {
         );
     }
 
+    /// Paste steps as linked references to the originals.
     pub fn link_paste_steps(&mut self) {
         let Some(copied) = self.editor_ctx.copied_steps.take() else {
             self.ui.set_status("Nothing copied".to_string());