feat(chargen): Campaign CC slice CC6a — index→ObjDesc factory + preview renderer foundation

Delivers the CC6a foundation half of the chargen 3D preview: the missing
index->ObjDesc appearance factory the campaign plan's acdream-seams
section named, plus a static-pose offscreen renderer following
PrivateEntityViewportRenderer's proven paperdoll/appraisal architecture.
Page mount, spin/color-wheel controls, and rotate/zoom behavior stay out
of scope per the CC4-parallel worktree contract (CC6b, after CC4 merges).

Core (src/AcDream.Core/CharGen/, pure, no Chorizite on public surfaces):
ChargenAppearanceFactory.TryCompose ports gmCG3DView::Update @0x004EE9D0's
ObjDesc rebuild in its exact decompiled order - base body, hair style,
clothing in retail's own Headgear/Trousers/Shirt/Footwear order (not the
UI tab order or the wire's field order, both of which differ), eyes
(bald-aware), nose, mouth, then the unconditional skin subpalette, hair
color, eye color. ChargenPalSetMath ports PalSet::GetPaletteID's
shade-to-index formula, cross-checked three ways (decomp control flow,
ACE's PaletteSet.GetPaletteID "Taken from acclient.c" citation, ACViewer's
identical slider math). ChargenPalSet/ChargenClothingTable are pure
projections behind IChargenPalSetSource/IChargenClothingTableSource so the
factory itself never touches a dat.

Content (src/AcDream.Content/CharGen/): ChargenAppearanceCatalog is the
cached dat-backed implementation of those two source interfaces, mirroring
ChargenTableReader's no-leak discipline.

App (src/AcDream.App/Rendering/): ChargenPreviewRenderer is a third facade
over PrivateEntityViewportRenderer beside PaperdollViewportRenderer and
CreatureAppraisalViewportRenderer - no existing rendering file touched.
ChargenPreviewCamera carries the four retail-verbatim per-heritage eye
profiles from gmCGAppearancePage::Update @0x0047E8F0 (cross-checked
against ZoomIn/ZoomOut's identical literals) plus the recovered rotation
(3.0 s/revolution) and zoom-tween (0.6 s, reconstructed from the
decompiler's garbled float literals - the plan's own "measure if it
matters" note is resolved, not garbled beyond recovery). Rotation applies
to the character model, not the camera, per gmCGAppearancePage::DoRotation.
ChargenPreviewEntityBuilder resolves Setup/GfxObj/Surface/Animation itself
(there is no live entity yet), reusing DatLiveEntityProjectionMaterializer's
surface-override algorithm and RetailPaperdollPoseApplicator's held-pose
technique, generalized to chargen's per-heritage rest-pose DID.

Two register rows filed: TS-83 (the plan-named CC6a static-pose-vs-retail-
idle-loop staging, CC6b to retire) and TS-82 (measured, not assumed - the
un-ported clothing Setup-substitution fallback chain costs nothing for the
9 standard heritages with clothing UI, but Undead's default gear choices
genuinely lack ClothingBaseEffects coverage for Undead's own body Setup).

Tests: ChargenPalSetMathTests, ChargenAppearanceFactoryTests (hand-built
fixtures), ChargenAppearanceCatalogInstalledDatTests (installed-DAT sweep,
all 26 heritage/gender combinations, zero missing PalSet/ClothingTable
ids), ChargenPreviewCameraTests, ChargenPreviewEntityBuilderTests
(installed-DAT-gated, proves a real 34-part Aluvian mesh resolves).
Core.Tests 4767/1 skip, Content.Tests 146/0, App.Tests 5121/6 skips - all
pre-existing skips, zero failures, full solution Release build green.

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

src/AcDream.Core/CharGen/ChargenPalSetMath.cs

@@ -0,0 +1,49 @@
+namespace AcDream.Core.CharGen;
+
+/// <summary>
+/// Pure port of retail's shade→palette-index resolution
+/// (<c>PalSet::GetPaletteID @ 0x005AC570</c>, invoked from
+/// <c>gmCG3DView::Update @ 0x004EE9D0</c> for the skin/hair subpalette
+/// build and from <c>ClothingTable::BuildObjDesc @ 0x005A7900</c> for every
+/// clothing-slot dye choice). The decompiled body is FPU-elided (the x87
+/// bounds-compare against 0.0/1.0 and the truncating <c>_ftol2()</c> cast
+/// lose their operands to the decompiler), but ACE's
+/// <c>ACE.DatLoader.FileTypes.PaletteSet.GetPaletteID</c> carries the
+/// explicit comment "Taken from acclient.c (PalSet::GetPaletteID)" with the
+/// exact formula below — corroborated by the decomp's own control-flow
+/// shape (a two-sided FPU compare consistent with a <c>[0,1]</c> bounds
+/// check, then one truncating cast) and independently by ACViewer's
+/// <c>ClothingTableList.xaml.cs:97</c> UI slider, which reimplements the
+/// identical <c>(count - 0.000001) * shade</c> expression for its own shade
+/// preview. Three independent sources agree.
+/// </summary>
+public static class ChargenPalSetMath
+{
+    /// <summary>
+    /// Resolves a shade fraction to an index into a palette-id list of the
+    /// given <paramref name="count"/>. Returns -1 (retail's
+    /// <c>INVALID_DID</c> outcome) when <paramref name="count"/> is
+    /// non-positive or <paramref name="shade"/> falls outside
+    /// <c>[0.0, 1.0]</c> — including retail's own <c>-1.0</c> "unset"
+    /// sentinel (<c>CharGenState::Reset @ 0x005C68A0</c>), which is
+    /// deliberately out of range so an untouched shade resolves to
+    /// "nothing," matching retail. Callers should treat -1 as "skip this
+    /// subpalette contribution" rather than emit a placeholder id.
+    /// </summary>
+    public static int GetPaletteIndex(int count, double shade)
+    {
+        if (count <= 0 || shade < 0.0 || shade > 1.0)
+            return -1;
+
+        // Truncating cast, exactly as ACE's cited port and the decomp's
+        // _ftol2() (which truncates toward zero on x86, matching a plain
+        // C-style (int) cast here since count > 0 and 0 <= shade <= 1 keep
+        // the product non-negative).
+        int index = (int)((count - 0.000001) * shade);
+        if (index < 0)
+            index = 0;
+        if (index > count - 1)
+            index = count - 1;
+        return index;
+    }
+}