Refactor afterSetId in src/button/Base.mjs

The current implementation of afterSetId in src/button/Base.mjs mutates the class prototype's _vdom when called during the construction phase (before initConfig clones the VDOM).

Current Code:

afterSetId(value, oldValue) {
    super.afterSetId(value, oldValue);
    this.textNode.id = value + '__text';
}

Proposed Change:

1. Move the textNode.id assignment to an override of ensureStableIds().
2. ensureStableIds() is called by Component.Base#mergeConfig after _vdom has been cloned for the instance, ensuring safety.
3. Remove the manual assignment from afterSetId (or make it conditional, but Component.Base handles ensureStableIds on ID change if configs applied, so overriding ensureStableIds handles both init and update cases).

Goals:

• Eliminate prototype mutation.
• Ensure textNode IDs are stable and unique per instance.
• Add unit tests to verify the fix and prevent regression.