Add frameless window with custom drag regions (Obsidian-style)

Remove native macOS titlebar via decorations:false + titleBarStyle:overlay.
Add -webkit-app-region:drag to panel headers (Sidebar, NoteList, Editor tab
bar, Inspector) with no-drag on interactive elements. Sidebar header gets
78px left padding for macOS traffic light buttons.

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

src/components/NoteList.css

@@ -13,6 +13,13 @@
   display: flex;
   align-items: center;
   justify-content: space-between;
+  -webkit-app-region: drag;
+  app-region: drag;
+}
+
+.note-list__header button {
+  -webkit-app-region: no-drag;
+  app-region: no-drag;
 }
 
 .note-list__header h3 {