docs(user): update admin and collections instructions for sidebar UI

Admin:
- Admin pages live in the sidebar's Administration panel (Dashboard,
  Libraries, Hash Conflicts, Users, Settings)
- Library creation is the Create Library modal (Library Name,
  Description, Library Type); folders are added afterwards by expanding
  the library row and using the Folders section's path input + Browse +
  Add — the old Add Library modal with folder and 'Scan on save' fields
  no longer exists
- Scanning is via the Scanner API or watch mode (File Watcher status on
  the admin dashboard); remove references to the removed per-library
  Rescan button and 'Force Rescan' option

Collections:
- Fill in the empty creating/managing placeholders with the real flow:
  New Collection button, modal fields (name, description, icon grid,
  color swatches), per-collection edit/delete icon buttons, Restore
  System button, and dashboard-section visibility via Customize
  Dashboard

docs/user/admin-library-management.md

@@ -8,12 +8,12 @@ When creating or managing a library, you can add folders containing your media f
 
 The admin library page includes a folder browser to help you select folders on the server:
 
-1. Navigate to **Admin → Library Management**
-2. Find the library you want to manage
-3. Click the **Folders** button
-4. Click **Browse** next to "Add folder path"
+1. Open the **Administration** panel in the sidebar (admins only) and go to **Libraries**
+2. Click a library in the list to expand its panel
+3. Find the **Folders** section
+4. Click **Browse** next to the folder path input — this opens the **Browse Folders** dialog
 5. Navigate through the server's filesystem
-6. Select a folder by clicking **Select This Folder**
+6. Select a folder; it fills the path input, then click **Add**
 
 ### Security