fix: use consistent tag names across channels and add component gap

- Stable release tag changed from v01 to 'stable' for consistency
- All updates.xml channels now use channel name as tag
- Add 0.75rem margin below #maincontent component area

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

src/media/css/template.css

@@ -14994,6 +14994,10 @@ iframe {
 	margin-bottom: 0;
 }
 
+#maincontent {
+	margin-bottom: 0.75rem;
+}
+
 .container-component,
 .sidebar-left,
 .sidebar-right {