feat: skin engine + Twenty CRM theme for iistwin

- Add client/src/themes/ with tokens, built-in skins (iistwin, twenty, omegaprom)
- Add ThemeProvider with data-skin/data-theme and runtime CSS for custom skins
- Add npm run skins:generate script for build-time CSS generation
- Add organization_skins table, migration and CRUD API
- Add activeSkinId to organizations and expose it in /api/auth/me
- Add skin switcher in /profile and admin skin editor in /settings/appearance
- Adapt index.css hardcoded colors to skin tokens
- Update AGENTS.md and Obsidian notes

client/src/components/folders/FormFolderTree.tsx

@@ -295,8 +295,7 @@ function FolderNodeContent({
         isOver && 'ring-2 ring-primary bg-primary/10'
       )}
       style={{ paddingLeft: `${item.level * 16 + 8}px` }}
-      onClick={() => onSelectFolder(item.id)}
-      onDoubleClick={() => onToggleExpand(item.id)}
+      onClick={() => onToggleExpand(item.id)}
     >
       <button
         type="button"