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/routes/auth.py

@@ -19,7 +19,7 @@ def _issue_portal_cookie(user, response):
         'sub': user.username,
         'user_id': user.id,
         'email': user.email,
-        'role': 'admin' if user.is_admin else 'user',
+        'role': user.role,
         'apps': user.get_accessible_apps(),
         'iss': 'enterprise-digital-platform',
         'iat': now,
@@ -74,3 +74,40 @@ def logout():
     resp.delete_cookie(current_app.config['PORTAL_COOKIE_NAME'], path='/')
     flash('You have been signed out.', 'info')
     return resp
+
+
+@bp.route('/portal-return')
+def portal_return():
+    """
+    Re-establish a portal Flask-Login session from the JWT cookie.
+
+    Sub-apps link here instead of '/' so the user is always properly
+    logged in to the portal even if the session cookie expired while
+    they were working in a sub-app.
+    """
+    # Already logged in — just go to the dashboard
+    if current_user.is_authenticated:
+        return redirect(url_for('dashboard.index'))
+
+    token = request.cookies.get(current_app.config['PORTAL_COOKIE_NAME'])
+    if not token:
+        return redirect(url_for('auth.login'))
+
+    try:
+        payload = jwt.decode(
+            token,
+            current_app.config['PORTAL_JWT_SECRET'],
+            algorithms=['HS256'],
+            options={'require': ['exp', 'sub', 'user_id']},
+        )
+    except jwt.InvalidTokenError:
+        return redirect(url_for('auth.login'))
+
+    user = PortalUser.query.get(payload.get('user_id'))
+    if not user or not user.is_active:
+        return redirect(url_for('auth.login'))
+
+    login_user(user, remember=False)
+    resp = make_response(redirect(url_for('dashboard.index')))
+    _issue_portal_cookie(user, resp)   # refresh the JWT while we're here
+    return resp