feat: open note in new window (Cmd+Shift+Click / Cmd+Shift+O)

Add multi-window support: notes can be opened in dedicated secondary
Tauri windows with editor-only layout (no sidebar, no note list).

Triggers: Cmd+Shift+Click on notes, Cmd+K → "Open in New Window",
Cmd+Shift+O shortcut, Note → "Open in New Window" menu bar item.

Secondary windows have their own auto-save, theme, and wikilink
navigation. Closing a secondary window does not affect the main window.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/utils/openNoteWindow.ts

@@ -0,0 +1,23 @@
+import { isTauri } from '../mock-tauri'
+
+/**
+ * Opens a note in a new Tauri window with a minimal editor-only layout.
+ * In browser mode (non-Tauri), this is a no-op.
+ */
+export async function openNoteInNewWindow(notePath: string, vaultPath: string, noteTitle: string): Promise<void> {
+  if (!isTauri()) return
+
+  const { WebviewWindow } = await import('@tauri-apps/api/webviewWindow')
+  const label = `note-${Date.now()}`
+  const url = `index.html?window=note&path=${encodeURIComponent(notePath)}&vault=${encodeURIComponent(vaultPath)}&title=${encodeURIComponent(noteTitle)}`
+
+  new WebviewWindow(label, {
+    url,
+    title: noteTitle,
+    width: 800,
+    height: 700,
+    resizable: true,
+    titleBarStyle: 'Overlay',
+    hiddenTitle: true,
+  })
+}