feat(operator)!: support multiple controllers and selectors per entity

[kimpenhaus]

Summary

Add support for multiple controllers targeting the same entity type.

• Add [LabelSelector] and [FieldSelector] controller attributes.
• Add generator error KOG001 for conflicting selector attributes.
• Add WatchStrategy.PerController and the opt-in SharedPerEntity strategy.
• Add client-side selector matching through IClientSideEntitySelector<TEntity>.
• Give each controller its own watcher, queue, and reconciliation pipeline.
• Share parallelism limits and per-UID locking across controller pipelines.
• Route EntityQueue<TEntity> requeues to the active controller pipeline.
• Aggregate queue-depth metrics per entity type.
• Reject multiple controllers when using custom queue or leader-election strategies.
• Update tests, migration guidance, and operator documentation.

Closes #909.

Breaking changes

• Remove IEntityQueueFactory and EntityQueueFactory. Use reconciliation results or the scoped EntityQueue<TEntity> delegate for requeues.
• Add the required OperatorSettings.WatchStrategy property. Prefer OperatorSettingsBuilder, which supplies the default PerController strategy.
• Stop registering IReconciler<TEntity> and ITimedEntityQueue<TEntity> in DI for the default in-memory pipeline.
• Resolving EntityQueue<TEntity> outside a reconciliation scope is ambiguous and throws when multiple controller pipelines exist.
• Add a cachePartition parameter to custom ResourceWatcher<TEntity> and LeaderAwareResourceWatcher<TEntity> constructors.
• Add IEntityReconcileCoordinator<TEntity> to custom queue-background-service constructors.
• Add the concrete controller type to direct Reconciler<TEntity> construction.
• Report controllers declaring both [LabelSelector] and [FieldSelector] as generator error KOG001.