Use texture source as payload identity carrier

[esnya]

Summary

• Remove duplicated Identity / ColorProfile carriers from neutral and Resonite texture payloads.
• Use ITextureImportSource.Identity / ITextureImportSource.ColorProfile as the single source of truth for grouping, mapping, and test assertions.
• Remove encoded payload identity/color-profile override parameters so encoded payloads cannot disagree with their import source.

Why

This keeps texture identity at the upstream import-source boundary instead of duplicating the same value on payload wrappers. Raw payload constructors still accept an identity only because they create the in-memory source at that boundary; after construction, the source is the only carrier.

Verification

• dotnet restore PlateauResoniteLink.sln --locked-mode --disable-build-servers
• dotnet format whitespace . --folder --verify-no-changes
• dotnet build PlateauResoniteLink.sln --configuration Release --no-restore --disable-build-servers -m:1 -p:UseSharedCompilation=false
• dotnet test PlateauResoniteLink.sln --configuration Release --no-restore --verbosity normal -m:1 --disable-build-servers -p:UseSharedCompilation=false (1023 passed)
• Fake Live Sink canonical dump for plateau-13213-higashimurayama-shi-2020 / 53395325 / dem,bldg / grid completed. git diff --no-index against runtime/windows/resonite/semantic-baselines/type-dem-grid-projection-result/baseline-parent/higashi-53395325-dem-bldg-grid-geotiff.json showed the existing parent-stack dedicated-material delta (96 +75/-21), with no new texture-source identity shaped regression. The generated dump was deleted and is not committed.

Review Gate

• Base PR Type Resonite texture payload variants #354 is CLEAN, CI green, has PR-body THUMBS_UP, and has no review threads.
• Open PR merge states were rechecked before push; all listed open PRs were CLEAN.
• Explorer subagent launch was attempted for fresh local review but the thread limit was reached, so the main agent performed the scoped review.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

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[esnya]

Superseded by #340: these texture source/payload changes depend on the same upstream texture boundary and have been folded into the main-target #340 PR instead of keeping a dependent stack.