refactor(render): one group-creation seam, required foliage key field, first-frame wind snap (Campaign VM VM6 review 3)

Narrow re-review of a82959f1: APPROVE, with follow-ups. All items landed.

N2 (structural): (a) extracted the ONE shared InstanceGroup-from-key
construction seam, WbDrawDispatcher.CreateGroupFromKey(key, registration,
frame) — before this there were two near-identical `new InstanceGroup
{ ... }` initializers (GetOrCreateInstanceGroup and GetOrCreatePackedGroup)
that had already drifted once (the round-2 F1 bug). Both routes call it now;
CreateGroupFromKey's own `new()` is the only production InstanceGroup
construction site repo-wide, same precedent as AppendPackedInstance. (b)
GroupKey.FoliageFlags lost its `= 0u` default and moved before CullMode in
the declaration (CullMode keeps its default, C# requires optional params to
trail required ones), so a `new GroupKey(...)` that omits it is a compile
error. Fixed every real construction site the reorder/requirement touched:
the 2 production sites, ToKey (a reconstruction from InstanceGroup the
review didn't count but the reorder broke), and 5 test sites (one more than
the review's "4" — InstanceGroupClearTests had a second, implicit
target-typed `MakeKey` factory the original count missed). Verified by a
full solution build.

N1: added CreateGroupFromKey_CopiesFoliageFlagsFromTheKey
(InstanceGroupClearTests) — a key carrying FoliageFlags 0x2 in, the created
group's FoliageFlags 0x2 out. That test plus N2b's required field are what
actually guard the round-2 F1 blocker; reworded PackedDispatcherOracleTests'
existing test comment to say what IT proves (the classification-to-
BuildIndirectArrays-to-BatchData.flags path), not that it guards the
classifier.

N3: corrected the plan's round-2 paragraph — folding FoliageFlags into the
G2/G3 digest is correct and symmetric, but CompareClassifiedOutput only
runs from RenderScenePViewFrameProductController.BuildAndCompare, which has
no production caller anywhere in src/AcDream.App/, and both of
RenderScenePViewFrameProductTests's own callers construct the controller
without the optional dispatcher argument — so the fold catches nothing
until that oracle is wired to an actual caller.

N4: the plan's F6 note now names both classification caches — the classic
route's EntityClassificationCache.EntityCacheEntry (self-heals per entity
on its own next eviction) and the packed route's
PackedProjectionClassificationEntry/PackedClassifiedBatch.Key
(PackedProjectionClassificationCache.BeginFrame clears its entire cache in
one shot on a RenderSceneGeneration change) — and notes neither mechanism
is keyed to a pack switch specifically.

N5: deleted the now-unused single-generic ComputeEntityHasCutoutSubset<T>
overload; its 4 test call sites now use the two-generic, zero-alloc
overload with an unused int context and a static (_, value) => value
lambda, so there is exactly one ComputeEntityHasCutoutSubset to keep
correct.

A6 (reviewer-filed): ResolveFoliageWind's _windMean/_windGust started at 0
and always eased toward the weather target by clock delta, with no
distinction for a graph's first-ever advance. A pinned clock
(ACDREAM_SKY_PHASE_SECONDS, the offline pixel gate's determinism pin) never
advances between calls, so the wind reached only whatever fraction the
first (1-second-clamped) step produced and sat there forever; live, the
first 10 s after a graph is constructed (pack selection / login) spun up
from dead calm even though the weather already IS what it is. Fixed at the
root: the first advance (_windFrameSerial == -1, the constructor sentinel)
now snaps _windMean/_windGust straight to the target; every later advance
eases over WeatherSystem.TransitionSeconds exactly as before. Added a
SetWindClockSecondsOverrideForTesting seam (_windClockSecondsOverride is no
longer readonly) so a hermetic test can advance the pinned clock by an
exact amount between two resolves without a real-time Thread.Sleep; two new
tests prove the first-advance snap is exact and a second advance still
eases at the normal rate. The three existing indoor/wind-disabled/amplitude
gate tests pass unchanged.

Verify: Release build 0 warnings/0 errors. App hermetic-lane filter
6,046/0 failed. Core.Tests 4,695/0 failed. Full hermetic-filtered solution:
15,274/0 failed across 15 projects.

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

tests/AcDream.App.Tests/Rendering/Wb/InstanceGroupClearTests.cs

@@ -218,7 +218,8 @@ public class InstanceGroupClearTests
             IndexCount: 6,
             TextureSlot: Slot(0xAA),
             TextureLayer: 0,
-            Translucency: TranslucencyKind.Opaque);
+            Translucency: TranslucencyKind.Opaque,
+            FoliageFlags: 0u);
         var cached = new CachedBatch(
             key,
             Slot(0xAA),
@@ -235,6 +236,49 @@ public class InstanceGroupClearTests
             out _));
     }
 
+    /// <summary>
+    /// Campaign VM VM6 review fix round 3 (N1): this is the guard for the
+    /// round-2 F1 blocker (the packed classifier's InstanceGroup carried
+    /// FoliageFlags == 0 no matter what GroupKey.FoliageFlags said, because
+    /// GetOrCreatePackedGroup's own initializer never copied it). N2a
+    /// deleted that possibility structurally — CreateGroupFromKey is the
+    /// ONLY InstanceGroup-from-key construction site left in production,
+    /// used by BOTH the classic and packed routes — and N2b made
+    /// GroupKey.FoliageFlags a required constructor argument, so a future
+    /// caller cannot silently default it to 0 either. Together those two
+    /// changes are what actually guards F1; this test pins
+    /// CreateGroupFromKey's own copy so a regression there fails here
+    /// directly instead of only showing up as a visual "trees don't sway"
+    /// report.
+    /// </summary>
+    [Fact]
+    public void CreateGroupFromKey_CopiesFoliageFlagsFromTheKey()
+    {
+        var key = new GroupKey(
+            FirstIndex: 10,
+            BaseVertex: 2,
+            IndexCount: 18,
+            TextureSlot: Slot(0x77),
+            TextureLayer: 0,
+            Translucency: TranslucencyKind.ClipMap,
+            FoliageFlags: 0x2u,
+            CullMode: DatReaderWriter.Enums.CullMode.CounterClockwise);
+
+        WbDrawDispatcher.InstanceGroup group =
+            WbDrawDispatcher.CreateGroupFromKey(key, registration: 5, frame: 9);
+
+        Assert.Equal(0x2u, group.FoliageFlags);
+        Assert.Equal(5, group.Registration);
+        Assert.Equal(9, group.LastUsedFrame);
+        Assert.Equal(key.FirstIndex, group.FirstIndex);
+        Assert.Equal(key.BaseVertex, group.BaseVertex);
+        Assert.Equal(key.IndexCount, group.IndexCount);
+        Assert.Equal(key.TextureSlot, group.TextureSlot);
+        Assert.Equal(key.TextureLayer, group.TextureLayer);
+        Assert.Equal(key.Translucency, group.Translucency);
+        Assert.Equal(key.CullMode, group.CullMode);
+    }
+
     [Fact]
     public void FramePrune_RetiresOnlyGroupsAbsentForWholePreviousFrame()
     {
@@ -314,14 +358,14 @@ public class InstanceGroupClearTests
     }
 
     private static AcDream.App.Rendering.Gpu.GpuTextureSlot Slot(uint index) => new(index);
-
     private static GroupKey MakeKey(uint textureSlot) => new(
         FirstIndex: 0,
         BaseVertex: 0,
         IndexCount: 6,
         TextureSlot: Slot(textureSlot),
         TextureLayer: 0,
-        Translucency: TranslucencyKind.Opaque);
+        Translucency: TranslucencyKind.Opaque,
+        FoliageFlags: 0u);
 
     private static WbDrawDispatcher.InstanceGroup MakeGroup(
         TranslucencyKind translucency,