docs: CRUD editor example with Binder and signal-based UI state management

[platosha]

Fixes #5075

• Introduce CrudEditorExample demonstrating reactive CRUD functionality using signals, binder integration, and effects
• Add a guide article to UI state examples documentation

[tltv]

Maybe this could be reformed in such way that users should be aware of setBean meaning unbuffered binder, and changes to the bean are directly reflected to the signal value. This may be wanted in some use case, but usage of buffered binder with readBean (or readRecord for some other use case) is used for the explained reason in this example and it's recommended in this case when form fields are bound to signals.

[tltv]

Suggested change

	We use [methodname]`Binder::readBean(bean)` to update the form data using
	a signal. This is the preferred approach.
	Avoid using [methodname]`Binder::setBean(beanInstance)` with signals, as this
	enables the binder to change the bean properties directly using setter methods.
	Such changes are not detected by signals.
	To update the signal with the changes from the binder,
	use [methodname]`Binder::writeBean(bean)` combined with the `signal.set(bean)`,
	see the example below.
	This example uses [methodname]`Binder::readBean(bean)`, which copies the bean's
	property values into the form fields. Changes in the fields are held by the
	binder and only written back when you explicitly call
	[methodname]`Binder::writeBean(bean)`. This is the recommended approach when
	form fields bind to signals, because it gives you full control over when the
	signal value is updated (see the save example below).
	Using [methodname]`Binder::setBean(bean)` instead binds the form fields
	directly to the bean instance. Every field edit is written to the bean
	immediately via its setter methods. Those direct mutations are not detected by
	signals, so the signal value can change without triggering reactive updates.
	This may suit scenarios where immediate write-through is desired, but in most
	cases [methodname]`readBean` combined with [methodname]`writeBean` is
	preferred.