feat: 3-tier role system across all platform apps

Portal:
- Replace is_admin boolean with role column (admin/advanced/standard)
- Settings UI: 3-tier portal role select + per-app role dropdowns
- /portal-return endpoint: re-establishes session from JWT for sub-app back-links
- /api/internal/nv-users: internal endpoint for NetworkView user sync
- portal/migrate_roles.py: one-time DB migration script
- Role badges (admin/advanced/standard) in topbar and settings table

DigiServer:
- Add editor and viewer roles (portal advanced->editor, standard->viewer)
- PlaylistPermission model: grant viewer users edit access to specific playlists
- app/utils/access.py: shared editor_required, admin_required, can_edit_playlist helpers
- Content routes: editor_required on create/delete, per-playlist permission check on mutations
- Admin: playlist_permissions route + template to manage viewer playlist grants
- Base template: hide Admin nav for viewers, Portal button (⬡) returns to portal
- content_list_new: hide create/delete for viewers; Manage vs View button per permission
- manage_playlist_content: view-only mode when user lacks edit permission

NetworkView:
- backend/src/middleware/rbac.js: requireRole + requireWriteAccess helpers
- site_permissions table: one site per advanced user
- All mutating routes guarded (admin=all, advanced=assigned site, viewer=read-only)
- Portal SSO auto-upsert: user row synced from X-Auth-Role on every request
- GET /api/users: merges portal users list with local NV data (all 4 portal users visible)
- GET/PUT /api/users/:id/site-permission: assign site to advanced user
- Settings Users tab: role badges, site dropdown for advanced, (portal only) indicator
- Sidebar: ⬡ Portal button between Settings and Logout
- Frontend build: VITE_API_BASE=/networkview/api now set in start-dev.sh

IT Assets / Server Monitor:
- portal_sso.py updated: map advanced->editor/viewer, standard->readonly
- AdminUser model: add editor role + is_editor property

digiserver-v2/app/templates/admin/user_management.html

@@ -27,6 +27,7 @@
                     <th>Role</th>
                     <th>Created At</th>
                     <th>Last Login</th>
+                    <th>Permissions</th>
                 </tr>
             </thead>
             <tbody>
@@ -40,12 +41,22 @@
                             {% endif %}
                         </td>
                         <td>
-                            <span class="badge badge-{{ 'success' if user.role == 'admin' else 'secondary' }}">
+                            <span class="badge badge-{{ 'success' if user.role == 'admin' else ('warning' if user.role == 'editor' else 'secondary') }}">
                                 {{ user.role|capitalize }}
                             </span>
                         </td>
                         <td>{{ user.created_at | localtime if user.created_at else 'N/A' }}</td>
                         <td>{{ user.last_login | localtime if user.last_login else 'Never' }}</td>
+                        <td>
+                            {% if user.role == 'viewer' %}
+                            <a href="{{ url_for('admin.playlist_permissions', user_id=user.id) }}"
+                               class="btn btn-sm" style="font-size:12px; padding:4px 10px;">
+                                🎬 Playlists
+                            </a>
+                            {% else %}
+                            <span style="color:#999; font-size:12px;">all access</span>
+                            {% endif %}
+                        </td>
                     </tr>
                     {% endfor %}
                 {% else %}