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

portal/app/templates/settings/index.html

@@ -41,10 +41,12 @@
             <td><strong>{{ user.username }}</strong></td>
             <td class="text-muted">{{ user.email }}</td>
             <td>
-              {% if user.is_admin %}
+              {% if user.role == 'admin' %}
                 <span class="badge badge-admin">admin</span>
+              {% elif user.role == 'advanced' %}
+                <span class="badge badge-advanced">advanced</span>
               {% else %}
-                <span class="badge badge-user">user</span>
+                <span class="badge badge-user">standard</span>
               {% endif %}
             </td>
             <td class="text-muted">
@@ -80,9 +82,13 @@
                   <option value="none"  {% if not (cur_access and cur_access.is_active) %}selected{% endif %}>
                     — no access
                   </option>
-                  <option value="user"
-                    {% if cur_access and cur_access.is_active and (not cur_access.app_role or cur_access.app_role == 'user') %}selected{% endif %}>
-                    ✓ user
+                  <option value="standard"
+                    {% if cur_access and cur_access.is_active and cur_access.app_role == 'standard' %}selected{% endif %}>
+                    👁 standard
+                  </option>
+                  <option value="advanced"
+                    {% if cur_access and cur_access.is_active and cur_access.app_role == 'advanced' %}selected{% endif %}>
+                    ✏ advanced
                   </option>
                   <option value="admin"
                     {% if cur_access and cur_access.is_active and cur_access.app_role == 'admin' %}selected{% endif %}>