UX: Disable Add Comment toolbar button when no text is selected

[Copilot]

The "Add Comment" toolbar button was always enabled regardless of editor selection state, requiring a toast notification to communicate that no text was selected rather than preventing the action up front.

Changes

• Disabled state on load — postAceInit calls updateAddCommentButtonState(false) after plugin init so the button starts disabled
• Reactive to selection — aceEditEvent hook calls updateAddCommentButtonState(!checkNoTextSelected(rep)) on every selection change, enabling/disabling the button in real time
• Click guard — the .addComment click handler bails out early if the button is disabled (belt-and-suspenders alongside the CSS)
• Cached DOM refs — this.$addCommentBtn and this.$addCommentBtnLink are cached once in init() to avoid repeated lookups on the hot aceEditEvent path
• CSS — .addComment.disabled applies opacity: 0.4 + cursor: not-allowed; .addComment.disabled > a sets pointer-events: none to block clicks on the anchor without breaking Playwright's ability to interact with the <li>
• Tests — clickAddCommentButton helper now polls for enabled state before clicking; five new Playwright specs cover: initial disabled state, enabled on selection, re-disabled on deselection, click-while-disabled does not open form, click-while-enabled opens form

// New method on EpComments.prototype
EpComments.prototype.updateAddCommentButtonState = function (hasSelection) {
  const $btn = this.$addCommentBtn;
  const $a = this.$addCommentBtnLink;
  if (!$btn) return;
  if (hasSelection) {
    $btn.removeClass('disabled');
    $a.removeAttr('aria-disabled');
  } else {
    $btn.addClass('disabled');
    $a.attr('aria-disabled', 'true');
  }
};