Add plugin watchdog to auto-disable failing plugins

[tadelv]

Problem

plugin_loader_service.dart:160 has a FIXME noting that there's no watchdog for unloadable plugins. Currently there's a 1-second Future.any() timeout, but:

• If a plugin throws during load, it can still crash the caller
• There's no mechanism to auto-disable plugins that repeatedly fail to load
• A broken plugin can cause issues on every app restart

Current code

// FIXME: add watchdog so we don't break the app with unloadable plugins
await Future.any([
  pluginManager.loadPlugin(...),
  Future.delayed(Duration(seconds: 1), () {
    throw Exception("load timeout occured");
  }),
]);

Suggested improvement

• Wrap the load in a try-catch that records failures per plugin
• After N consecutive failures (e.g., 3), auto-disable the plugin and log a warning
• Provide a way to re-enable disabled plugins from the settings UI
• Consider adding a health check after load (e.g., verify plugin responded to onLoad)