docs(research): sky/weather investigation handoff + diagnostic tools

Captures everything learned from a long worktree iteration on the
foreground-rain bug (ISSUES.md #1 / #26) plus a new star-rendering
bug observed in the same area. The code work from that worktree
(WeatherDispatcher, EmitterDescLoader.LoadFromDat, WeatherCellRenderer,
GameWindow integration) was reverted because it didn't visibly fix
the rain bug — but the research findings + diagnostic tools are
durable and should not have to be rediscovered.

What's added:
- docs/research/2026-04-26-sky-investigation-handoff.md
  Comprehensive seed prompt for the next session. Covers:
  * Bug A: foreground rain (#26) — what's open, what's confirmed,
    what's been tried
  * Bug B: stars rendering as square in corner (NEW, user-observed)
  * 40-agent decomp scan findings — retail rain is NOT camera-
    particles, NOT server-driven, NOT screen-space; the mesh IS
    a hollow octagonal tube; only 5 weather GfxObjs in Dereth
  * Things ruled out by trial (envelope, scaling, unlit, depth-
    always alone, Setup loading)
  * Things to try next (depth+zfar combined, full render-state
    audit, frame ordering, star UV bug as easier first target)
  * Acceptance criteria for "done"

- docs/research/2026-04-26-chorizite-pr-draft.md
  Upstream PR draft for Chorizite/DatReaderWriter. Five generated
  DBObj source files reference nonexistent enum values and are
  silently excluded from the NuGet build:
  ParticleEmitterInfo, Clothing, PaletteSet, DataIdMapper,
  DualDataIdMapper. Fix: delete the duplicates. Independent of
  the rain work — benefits the AC modding ecosystem broadly.

- docs/research/2026-04-26-datreaderwriter-reference.md
  Developer reference for our DatReaderWriter usage. Version,
  types we consume, known broken types, thread-safety caveats,
  upgrade procedure, NuGet-vs-vendored decision matrix.

- tools/PesChainAudit/
  Recursive PES walker — given a 0x33xxxxxx script id, walks all
  CallPES references and dumps every hook + every referenced
  ParticleEmitter's parameters. Used to prove no weather PES
  emits rain particles.

- tools/TextureDump/
  Dumps texture pixel statistics (alpha histogram, brightness,
  max) and saves as PNG for visual inspection.

- tools/WeatherEnumerator/
  Enumerates every DayGroup in a Region, lists weather SkyObjects
  (Properties & 0x04), dumps GfxObj bounding boxes.

- tools/WeatherSetupProbe/
  Loads a Setup id, dumps each part's GfxObj + frame + scale +
  surface. Used to prove weather Setups are 5cm dummy carriers.

Worktree feature/sky-fixes is being deleted in a follow-up step.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tools/WeatherEnumerator/WeatherEnumerator.csproj

@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <RootNamespace>WeatherEnumerator</RootNamespace>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="C:\Users\erikn\source\repos\acdream\references\DatReaderWriter\DatReaderWriter\DatReaderWriter.csproj" />
+  </ItemGroup>
+
+</Project>