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/Layout/DatWidgetFactory.cs

@@ -10,11 +10,11 @@ namespace AcDream.App.UI.Layout;
 /// <see cref="UiDatElement"/>.
 ///
 /// <para>
-/// Type 12 elements that carry NO own state media (pure style prototypes /
-/// BaseElement stores) return null from <see cref="Create"/> and are skipped.
-/// Type 12 elements that DO carry own sprites (e.g. a chat element whose Type-0
-/// derived form inherited Type 12 from its base prototype) are rendered normally.
-/// See docs/research/2026-06-15-layoutdesc-format.md Correction 8.
+/// Type 12 = UIElement_Text — a scrollable colored-line text view. Every Type-12
+/// element is now built as a <see cref="UiText"/>. Elements that carry their own
+/// dat sprite media keep it as the <see cref="UiText.BackgroundSprite"/>. Pure
+/// prototype elements (no state media, no controller binding) draw nothing because
+/// <see cref="UiText.BackgroundColor"/> defaults to transparent.
 /// </para>
 ///
 /// <para>
@@ -45,23 +45,17 @@ public static class DatWidgetFactory
     /// Returns (0,0,0) when the texture is not yet uploaded.</param>
     /// <param name="datFont">Retail UI font for the meter's "cur/max" number overlay.
     /// May be null pre-load — the meter falls back to the debug bitmap font.</param>
-    /// <returns>The widget, or <c>null</c> for a pure Type-12 style prototype with no own sprites (caller skips it).</returns>
+    /// <returns>The widget for this element. Never null — every type produces a widget.</returns>
     public static UiElement? Create(ElementInfo info,
         Func<uint, (uint, int, int)> resolve, UiDatFont? datFont)
     {
-        // Type 12 = style prototype / BaseElement store referenced by BaseLayoutId.
-        // PURE prototypes (no own state media) are property bags — never rendered; skip them.
-        // A Type-12 element that carries its own state media (e.g. a chat Send button whose
-        // Type-0 derived element inherited Type 12 from its base prototype) has sprites to
-        // show and must render. See format doc §8 and the G1 task note.
-        if (info.Type == 12 && info.StateMedia.Count == 0) return null;
-
         UiElement e = info.Type switch
         {
             1  => new UiButton(info, resolve),         // UIElement_Button (reg :125828)
             6  => new UiMenu(),                        // UIElement_Menu (reg :120163)
             7  => BuildMeter(info, resolve, datFont),  // UIElement_Meter
             11 => new UiScrollbar(),                   // UIElement_Scrollbar (reg :124137)
+            12 => BuildText(info, resolve),            // UIElement_Text (reg :115655)
             _  => new UiDatElement(info, resolve),     // generic fallback for all other types
         };
 
@@ -178,4 +172,20 @@ public static class DatWidgetFactory
 
         return (left, tile, right);
     }
+
+    // ── Text ─────────────────────────────────────────────────────────────────
+
+    /// <summary>Type-12 UIElement_Text: a scrollable colored-line text view. The element's
+    /// own Direct/Normal media (if any) becomes the background sprite, drawn under the text —
+    /// so a Type-12 element that previously rendered via UiDatElement keeps its sprite. Lines
+    /// are bound later by the controller (LinesProvider). An unbound UiText draws nothing
+    /// because <see cref="UiText.BackgroundColor"/> defaults to transparent.</summary>
+    private static UiText BuildText(ElementInfo info, Func<uint, (uint, int, int)> resolve)
+    {
+        uint bg = info.StateMedia.TryGetValue(
+                      !string.IsNullOrEmpty(info.DefaultStateName) ? info.DefaultStateName
+                    : info.StateMedia.ContainsKey("Normal") ? "Normal" : "", out var m)
+                  ? m.File : 0u;
+        return new UiText { BackgroundSprite = bg, SpriteResolve = resolve };
+    }
 }