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>

src/AcDream.App/Rendering/Wb/WbDrawDispatcher.PackedOracle.cs

@@ -669,8 +669,8 @@ public sealed unsafe partial class WbDrawDispatcher
                 texture.Slot,
                 texture.Layer,
                 translucency,
-                batch.CullMode,
-                foliageFlags);
+                FoliageFlags: foliageFlags,
+                CullMode: batch.CullMode);
             var classified = new PackedClassifiedBatch(
                 key,
                 restPose,
@@ -796,29 +796,16 @@ public sealed unsafe partial class WbDrawDispatcher
                 "Packed instance-group registration space was exhausted.");
         }
 
-        group = new InstanceGroup
-        {
-            FirstIndex = key.FirstIndex,
-            BaseVertex = key.BaseVertex,
-            IndexCount = key.IndexCount,
-            TextureSlot = key.TextureSlot,
-            TextureLayer = key.TextureLayer,
-            Translucency = key.Translucency,
-            CullMode = key.CullMode,
-            // Campaign VM VM6 review fix round 2 (F1 BLOCKER): this was the
-            // missing copy. GetOrCreateInstanceGroup (the classic route) has
-            // set FoliageFlags from key.FoliageFlags since the round-1
-            // fix; this packed-route sibling never did, so every packed
-            // production InstanceGroup carried FoliageFlags == 0 regardless
-            // of what ClassifyPackedBatches computed into the key —
-            // BatchData.flags bits 1/2 were always 0 for production world
-            // geometry even though the independently-classified shadow
-            // caster set them correctly, so casters swayed while the
-            // meshes they shadowed did not.
-            FoliageFlags = key.FoliageFlags,
-            Registration = _nextPackedGroupRegistration++,
-            LastUsedFrame = _packedGroupFrame,
-        };
+        // Campaign VM VM6 review fix round 3 (N2a): both routes share the
+        // ONE InstanceGroup-from-key seam now — see CreateGroupFromKey's
+        // doc comment. This is exactly the seam that closed the F1 bug
+        // (FoliageFlags copied on the classic side, dropped here) by
+        // construction: there is now exactly one place either route can
+        // build an InstanceGroup, and it always copies every GroupKey field.
+        group = CreateGroupFromKey(
+            key,
+            registration: _nextPackedGroupRegistration++,
+            frame: _packedGroupFrame);
         _packedGroups.Add(key, group);
         return group;
     }