feat: add macOS View menu with panel visibility items

- Create menu.rs module with View submenu
- Items: Editor Only (⌥1), Editor + Notes (⌥2), All Panels (⌥3)
- Emits 'menu-event' to frontend, handled by useViewMode hook
- Menu only created on desktop builds (#[cfg(desktop)])

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src-tauri/src/lib.rs

@@ -2,6 +2,7 @@ pub mod ai_chat;
 pub mod frontmatter;
 pub mod git;
 pub mod github;
+pub mod menu;
 pub mod settings;
 pub mod vault;
 
@@ -123,6 +124,7 @@ pub fn run() {
             {
                 app.handle().plugin(tauri_plugin_updater::Builder::new().build())?;
                 app.handle().plugin(tauri_plugin_process::init())?;
+                menu::setup_menu(app)?;
             }
 
             // Purge trashed files older than 30 days on startup

src-tauri/src/menu.rs

@@ -0,0 +1,30 @@
+use tauri::{menu::SubmenuBuilder, App, Emitter};
+
+const VIEW_ITEMS: [(&str, &str, &str); 3] = [
+    ("view-editor-only", "Editor Only", "Alt+1"),
+    ("view-editor-list", "Editor + Notes", "Alt+2"),
+    ("view-all", "All Panels", "Alt+3"),
+];
+
+pub fn setup_menu(app: &App) -> Result<(), Box<dyn std::error::Error>> {
+    let mut view_menu = SubmenuBuilder::new(app, "View");
+    for (id, label, accel) in &VIEW_ITEMS {
+        view_menu = view_menu.text(*id, format!("{label}   {accel}"));
+    }
+    let view_submenu = view_menu.build()?;
+
+    let menu = tauri::menu::MenuBuilder::new(app)
+        .item(&view_submenu)
+        .build()?;
+
+    app.set_menu(menu)?;
+
+    app.on_menu_event(|app_handle, event| {
+        let id = event.id().0.as_str();
+        if id.starts_with("view-") {
+            let _ = app_handle.emit("menu-event", id);
+        }
+    });
+
+    Ok(())
+}