fix(ui): OP2 re-review closure (coordinator pass) — AP-195, tooltip port, zero-children pin

Closes the mechanism lens's REOPEN (one MUST-FIX) and both lenses' small
residuals on the OP2 rework (b236a442); the blast lens re-review was
CLOSED outright. Fable-direct per the two-failure escalation rule.

- AP-195 filed: UIOption_CheckboxBitfield64 ports HALF of Refresh
  @0x004859C0 — the ANY-set checkbox predicate is exact, but the ALL-set
  LED media swap (P0x10000082=0x06004D17 / P0x10000083=0x06004D19) and
  the ListBox self-sizing tail (ResizeTo/CalculatePaperSize — the block
  IS a UIElement_ListBox in retail) are unported, and the block's row
  stacking is a second divergent implementation beside UiTemplateListBox.
  All due at OP5 before the Chat tab's connected gate; the IsSet doc
  comment now names both halves instead of quoting only the ported one.
- Row tooltips: UiButton gains settable TooltipText surfaced through the
  shared GetTooltipText hover pipeline (UiCatalogSlot's pattern);
  UiCheckboxBitfield64.AddChild applies the row tooltip retail stamps in
  CreateChildren @0x00485DF0, and documents that the 0x10000084 row-index
  attribute stamp is deliberately replaced by the typed mask closure.
- AD-73 addendum: UiTemplateListBox.ConsumesDatChildren=true is inert
  only while no authored Type-5 element carries children — that premise
  is now conformance-PINNED across all 32 fixtures (a future DAT
  regeneration surfacing an authored child fails the build instead of
  silently dropping it).
- Plan doc: OP2's contract names UiTabPanel.cs (retail UIElement_Panel),
  not the fictional-class-named UiTabControl.cs; ledger records OP1 and
  OP2 both CLOSED.

Full Release suite: 12,871 passed / 4 skipped / 0 failed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/AcDream.App/UI/UiButton.cs

@@ -88,6 +88,17 @@ public sealed class UiButton : UiElement, IUiGlobalTimeListener, IUiDatStateful
     /// <summary>Label color (default white).</summary>
     public Vector4 LabelColor { get; set; } = Vector4.One;
 
+    /// <summary>Settable tooltip, surfaced through the shared
+    /// <see cref="UiElement.GetTooltipText"/> hover pipeline (same pattern as
+    /// <see cref="UiCatalogSlot"/>). Retail option rows stamp theirs via
+    /// <c>UIElement::SetTooltip</c> during row construction
+    /// (e.g. <c>UIOption_CheckboxBitfield64::CreateChildren @0x00485DF0</c>).</summary>
+    public string? TooltipText { get; set; }
+
+    /// <inheritdoc />
+    public override string? GetTooltipText() =>
+        string.IsNullOrWhiteSpace(TooltipText) ? null : TooltipText;
+
     /// <summary>Retail LayoutDesc property <c>0x21</c> (two-pass glyph outline,
     /// <c>UIElement_Text::SetOutline @0x0046a81c</c>). Seeded by DatWidgetFactory
     /// from the element's effective-default state, same as <see cref="UiText.Outline"/>