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/new_user.html

@@ -34,13 +34,13 @@
           <label class="form-label">Password</label>
           <input type="password" name="password" class="form-input" required />
         </div>
-        <div class="form-group form-group--check">
+        <div class="form-group">
           <label class="form-label">Portal Role</label>
-          <label class="toggle">
-            <input type="checkbox" name="is_admin" />
-            <span class="toggle-slider"></span>
-            <span class="toggle-label">Platform administrator</span>
-          </label>
+          <select name="portal_role" class="form-select">
+            <option value="standard">Standard User — read-only access in apps</option>
+            <option value="advanced">Advanced User — create &amp; edit content in apps</option>
+            <option value="admin">Administrator — full access + user management</option>
+          </select>
         </div>
       </div>
 
@@ -61,8 +61,9 @@
             <select name="role_{{ app['id'] }}" class="form-select app-role-new-select"
                     data-color="{{ app.color }}">
               <option value="none">— No access</option>
-              <option value="user">✓ User</option>
-              <option value="admin">★ Admin</option>
+              <option value="standard">👁 Standard — read-only</option>
+              <option value="advanced">✏ Advanced — create &amp; edit</option>
+              <option value="admin">★ Admin — full access</option>
             </select>
           </div>
           {% endfor %}