feat(rnotes): convert to Docmost-style persistent sidebar layout

Replace 3-step drill-down navigation (notebook grid → note list → editor)
with a persistent sidebar showing collapsible notebook tree alongside the
editor. Sidebar supports search, per-notebook note lists, hover add buttons,
and active note highlighting. Mobile collapses to slide-in overlay <768px.

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

modules/rnotes/components/notes.css

@@ -2,6 +2,6 @@
 folk-notes-app {
 	display: block;
 	min-height: 400px;
-	padding: 20px;
+	padding: 0;
 	position: relative;
 }