Fix mx-step WC "Step +1" counter not incrementing in section 6.a

[Copilot]

The mx-step Web Component dispatched step-picked with this._value + 1 on every click but never mutated this._value, so every click emitted step: 1 and the counter appeared frozen.

Changes

• mx-step onclick — increment this._value in-place and update the shadow <output> before dispatching, so consecutive clicks accumulate:

  // Before
  () => this.dispatchEvent(new CustomEvent('step-picked', { detail: { step: this._value + 1 } }))
  
  // After
  () => {
    this._value += 1;
    this.shadowRoot.querySelector('output').textContent = '' + this._value;
    this.dispatchEvent(new CustomEvent('step-picked', { detail: { step: this._value } }));
  }

• mx-step element binding — added data-m-ex:wc-step@wc-picked="'' + val" to close the feedback loop: when the wc-picked store updates from the custom event, wc-step is also updated, keeping the "WC default value prop" <span> in sync.

• Fixes Fix the wc 'Step +1' in the index.html notebook #144

[dadhi]

Why do we need this code? Can we use the dmax for that?

[Copilot]

Good point. The manual _value mutation and textContent update are now replaced with a call to this.value = this._value + 1, which reuses the existing value setter that already handles both. The dmax binding data-m-ex:.@wc-step will also drive the setter when the wc-step store updates (via the wc-picked feedback binding), keeping everything in sync.