Add hybrid-duplication-audit skill

[timt-unity3d]

Summary

• Adds Skills/hybrid-duplication-audit, a Claude Code skill that audits asset duplication across the AssetBundle / ContentDirectory boundary in a hybrid Addressables 4.x build (some groups build to .bundle files, others build through BuildPipeline.BuildContentDirectory).
• The skill runs one analyze invocation combining the Addressables build layout report with the content directory build output, then matches source-asset paths across addressables_build_explicit_assets / addressables_build_data_from_other_assets and content_layout_source_assets to find what's genuinely duplicated.
• Matching by asset path (rather than object CRC) catches cases a plain CRC diff misses — for example the same shader built with a different variant set on each side, which is also why Addressables' own DuplicatedAssetCount can read 0 even when real cross-boundary duplication exists.
• Adds short cross-links in README.md, AGENTS.md, and Documentation/analyzer.md for discoverability, following this repo's existing manual-index convention.

Test plan

• Built UnityDataTool from this branch and ran Skills/hybrid-duplication-audit/scripts/Compare-HybridDuplication.ps1 against a real hybrid Addressables project, confirming it reproduces a hand-verified duplication total (three shared shaders, 214,824 bytes) exactly.
• Ran the script against a content-directory-only (non-hybrid) build and confirmed it reports "this is not a hybrid build" cleanly rather than a misleading result.
• Verified -KeepDatabase preserves the generated database and its tables are as documented.
• Reviewer sanity-check: run the script against your own hybrid Addressables project.