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/utils/access.py

@@ -0,0 +1,64 @@
+"""
+Shared role / access helpers for DigiServer blueprints.
+
+Import these instead of duplicating decorators in every blueprint.
+"""
+from functools import wraps
+from flask import abort, flash, redirect, url_for
+from flask_login import current_user
+
+
+# ── Role-gate decorators ──────────────────────────────────────────────────────
+
+def editor_required(f):
+    """Allow admin and editor roles; redirect viewers with a flash message."""
+    @wraps(f)
+    def decorated(*args, **kwargs):
+        if not current_user.is_authenticated:
+            return redirect(url_for('auth.login'))
+        if current_user.role not in ('admin', 'editor'):
+            flash('You need editor or admin privileges to perform this action.', 'danger')
+            return redirect(url_for('main.dashboard'))
+        return f(*args, **kwargs)
+    return decorated
+
+
+def admin_required(f):
+    """Allow admin role only."""
+    @wraps(f)
+    def decorated(*args, **kwargs):
+        if not current_user.is_authenticated:
+            return redirect(url_for('auth.login'))
+        if current_user.role != 'admin':
+            flash('Administrator access required.', 'danger')
+            return redirect(url_for('main.dashboard'))
+        return f(*args, **kwargs)
+    return decorated
+
+
+# ── Playlist permission check ─────────────────────────────────────────────────
+
+def can_edit_playlist(user, playlist_id: int) -> bool:
+    """
+    Return True if *user* is allowed to edit the given playlist.
+
+    - admin / editor  → always True
+    - viewer          → True only when a PlaylistPermission row exists
+    """
+    if user.role in ('admin', 'editor'):
+        return True
+    from app.models.playlist_permission import PlaylistPermission
+    return PlaylistPermission.query.filter_by(
+        user_id=user.id, playlist_id=playlist_id
+    ).first() is not None
+
+
+def get_editable_playlist_ids(user) -> set:
+    """Return the set of playlist IDs the user may edit (used in list views)."""
+    if user.role in ('admin', 'editor'):
+        # Import here to avoid circular imports at module load time
+        from app.models.playlist import Playlist
+        return {p.id for p in Playlist.query.with_entities(Playlist.id).all()}
+    from app.models.playlist_permission import PlaylistPermission
+    rows = PlaylistPermission.query.filter_by(user_id=user.id).all()
+    return {r.playlist_id for r in rows}