feat(web): weekly automatic updates with health check and rollback

A General-tab toggle (off by default) checks for and installs LEDMatrix and
plugin updates once a week, overnight in the configured timezone.

- Pre-update checks skip (and report) instead of forcing: local edits or
  commits, merge/live rebase, no upstream, low disk, missing health check, or
  a version that was already rolled back. An abandoned rebase (HEAD back on a
  branch) is cleared, since it would otherwise block every pull.
- The pull reuses the Update Code path (now perform_core_update(), which
  reports dependency install failures as data).
- ledmatrix-update-verify.service, started via a .path unit from a request
  file, restarts the services from its own cgroup, requires them to come up
  and stay up, and otherwise resets to the previous commit and reinstalls the
  previous requirements. It runs a copy of the checker taken before the pull.
- No SSH needed: switching the toggle on restarts the display service, which
  (as root) installs the two units from the repo templates for the web user.
  first_time_install.sh installs them too and takes --enable-auto-update /
  LEDMATRIX_AUTO_UPDATE (passed through by one-shot-install.sh).
- Plugins update after the code passes its check; failures, blocks and
  rollbacks raise an Overview banner and show under the toggle.

Tested end to end on a Pi: web-UI setup, a good update, a broken web service
and a broken display (both rolled back), a blocked local edit, and an
abandoned rebase found on the device.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

web_interface/blueprints/api_v3/config.py

@@ -454,16 +454,21 @@ def save_main_config():
 
         # Merge with existing config (similar to original implementation)
         current_config = api_v3.config_manager.load_config()
+        was_auto_update_enabled = bool((current_config.get('auto_update') or {}).get('enabled'))
 
         # Handle general settings
         # Note: Checkboxes don't send data when unchecked, so we need to check if we're updating general settings
         # If any general setting is present, we're updating the general tab
         is_general_update = any(k in data for k in ['timezone', 'city', 'state', 'country', 'web_display_autostart',
-                                                     'auto_discover', 'auto_load_enabled', 'development_mode', 'plugins_directory'])
+                                                     'auto_discover', 'auto_load_enabled', 'development_mode', 'plugins_directory',
+                                                     'auto_update_enabled'])
 
         if is_general_update:
             # For checkbox: if not present in data during general update, it means unchecked
             current_config['web_display_autostart'] = _coerce_to_bool(data.get('web_display_autostart'))
+            if not isinstance(current_config.get('auto_update'), dict):
+                current_config['auto_update'] = {}
+            current_config['auto_update']['enabled'] = _coerce_to_bool(data.get('auto_update_enabled'))
 
         if 'timezone' in data:
             current_config['timezone'] = data['timezone']
@@ -1033,7 +1038,7 @@ def save_main_config():
             if key in ['timezone', 'city', 'state', 'country',
                        'web_display_autostart', 'auto_discover',
                        'auto_load_enabled', 'development_mode',
-                       'plugins_directory', 'target_fps']:
+                       'plugins_directory', 'target_fps', 'auto_update_enabled']:
                 continue
             # Skip fields that are already handled above in their own named sections.
             # Without this, every form field name lands as a top-level config key too.
@@ -1068,7 +1073,17 @@ def save_main_config():
         except ImportError:
             pass
 
-        return success_response(message='Configuration saved successfully')
+        message = 'Configuration saved successfully'
+        # Switching automatic updates on finishes their setup, which needs
+        # the display service to restart (web_interface/auto_update.py).
+        try:
+            from web_interface import auto_update
+            note = auto_update.start_setup_if_needed(was_auto_update_enabled, current_config)
+            if note:
+                message = f'{message}. {note}'
+        except Exception:
+            logger.warning("Automatic update setup could not be started", exc_info=True)
+        return success_response(message=message)
     except Exception as e:
         logger.error("Error saving config", exc_info=True)
         return error_response(