feat(D.2b): UiText (Type 12) -- generic text + Type-12 flip; transcript factory-built (widget-generalization Task 5)

Rename UiChatView -> UiText (the retail UIElement_Text class,
RegisterElementClass(0xc) @ acclient_2013_pseudo_c.txt:115655).

Factory changes (DatWidgetFactory.cs):
- Remove the Type-12 skip (was: no-media -> null, with-media -> UiDatElement).
- Add Type 12 -> BuildText() -> UiText in the switch.
- BuildText extracts the element's Direct/Normal sprite as BackgroundSprite
  so any dat-media the element carried keeps rendering under the text.

UiText changes (renamed from UiChatView.cs):
- BackgroundColor default: (0,0,0,0.35) -> (0,0,0,0) (transparent).
  An unbound UiText draws nothing; the controller opts in to the translucent bg.
- New BackgroundSprite + SpriteResolve: optional dat state-sprite background
  drawn UNDER DrawFill+text (faithful UIElement_Text media support).

ChatWindowController.cs (Task 5 Step 8):
- Transcript property: UiChatView -> UiText.
- Bind() now uses layout.FindElement(TranscriptId) as UiText (factory-built)
  instead of manually constructing + AddChild-ing a new UiChatView.
- Sets BackgroundColor = (0,0,0,0.35) on the found widget (retail translucent bg).
- Removes the tInfo null-check from the early guard (transcript is factory-built;
  iInfo lookup kept for the input widget which is still manually constructed).
- BuildLines: UiChatView.Line -> UiText.Line throughout.

Vitals frozen: the Type-12 vitals number elements are meter children and are
never recursed by BuildWidget (the `if (w is not UiMeter)` gate), so they are
not built as widgets and keep rendering via UiMeter.Label. Vitals fixture
vitals_2100006C.json unchanged; LayoutConformanceTests + VitalsBindingTests green.

Tests:
- UiChatViewTests.cs -> UiTextTests.cs (class: UiTextTests, all UiChatView.* -> UiText.*)
- UiChatViewDatFontTests.cs -> UiTextDatFontTests.cs (same)
- DatWidgetFactoryTests: delete Type12_StylePrototype_ReturnsNull +
  DatWidgetFactory_Type12WithMedia_Renders; add Type12_Text_MakesUiText +
  DatWidgetFactory_Type12_AlwaysMakesUiText.
- LayoutImporterTests: BuildFromInfos_Type12Child_IsSkipped_Type3Present updated
  to assert IsType<UiText> (element is now in tree, transparent, not skipped).

Divergence register: AP-37 amended -- removed the "standalone Type-0 text
elements skipped / dat-text widget is Plan 2" clause (now shipped as UiText);
kept the meter-collapse clause and the vitals-numbers-via-UiMeter.Label clause.
AP-38/AP-39/AD-28 file references updated UiChatView.cs -> UiText.cs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.App/UI/UiScrollable.cs

@@ -7,7 +7,7 @@ namespace AcDream.App.UI;
 /// the scroll offset is an integer pixel value (<c>m_iScrollableY</c>) clamped to
 /// [0, ContentHeight - ViewHeight]; the thumb ratio is view/content; the position
 /// ratio is scroll/(content-view). Pure (no GL) so it is fully unit-tested and
-/// shared by the transcript (UiChatView) and the scrollbar (UiScrollbar).
+/// shared by the transcript (UiText) and the scrollbar (UiScrollbar).
 /// Decomp anchors: SetScrollableXY @0x4740c0, UpdateScrollbarSize_ @0x4741a0,
 /// UpdateScrollbarPosition_ @0x473f20, UIElement_Text::InqScrollDelta @0x4689b0.
 /// </summary>