Add find-package-skill registry for package-specific skills

.github/skills/find-package-skill/SKILL.md

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+---
+name: find-package-skill
+description: '**UTILITY SKILL** — Must be consulted before making any changes to packages under sdk/. Provides package-specific domain knowledge that prevents common mistakes. WHEN: add feature to package; fix bug in package; modify package code; regenerate from typespec; change client library.'
+---
+
+# Find Package Skill
+
+Before modifying any SDK package in this monorepo, check this registry to see
+if a package-specific skill exists. Package skills contain tribal knowledge
+(architecture, data flows, type mappings, pitfalls) that prevents common mistakes.
+
+Always check this registry before modifying any SDK package — even if you think
+you already know the package well.
+
+## How to Use
+
+1. Find the package you're modifying in the table below.
+2. Read the SKILL.md at the listed path using the Read tool. Then read all files under the `references/` directory next to it for additional context.
+3. If the package isn't listed, no package-specific skill exists yet — proceed normally.
+
+## Package Skills
+
+| Package                    | Path                                                                                              |
+| -------------------------- | ------------------------------------------------------------------------------------------------- |
+| `azure-search-documents`   | `sdk/search/azure-search-documents/.github/skills/search-documents/SKILL.md`                      |

sdk/search/azure-search-documents/.github/skills/search-documents/SKILL.md

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+---
+name: search-documents
+description: 'Post-regeneration customization guide for azure-search-documents SDK. After running tsp-client update, consult this skill to re-apply search-specific customizations and produce a production-ready SDK. WHEN: regenerate search SDK; search tsp-client update; fix search customization errors; search API version update; search SDK release; update search service version.'
+---
+
+# azure-search-documents — Package Skill
+
+<!-- TODO: Domain experts should fill in the sections below with tribal knowledge
+     specific to this package. -->
+
+## Common Pitfalls
+
+<!-- TODO: List the most dangerous mistakes an agent can make with this package.
+     Put these BEFORE the workflow — agents read them first. -->
+
+## Architecture
+
+<!-- TODO: High-level layout. Where does generated code live? What's hand-authored?
+     How do they interact? Document the customizations/ directory and SearchCustomizations.java. -->
+
+### Source Layout
+
+<!-- TODO: Show the directory tree. Mark files as GENERATED vs hand-written. -->
+
+### Generated vs Custom Code
+
+<!-- TODO: Explain the @Generated annotation. Methods WITH @Generated are auto-updated
+     by the generator. Methods WITHOUT @Generated in generated files are hand-written
+     convenience wrappers that need manual updates after regeneration. -->
+
+## Regeneration Workflow
+
+<!-- TODO: The exact commands to regenerate. What breaks after regeneration?
+     What needs manual fixup? Include gated phases. -->
+
+## Key Files
+
+<!-- TODO: The files an agent should read before making changes, and what each one does.
+     Include tsp-location.yaml, SearchCustomizations.java, pom.xml, CHANGELOG.md. -->
+
+## Service Version Management
+
+<!-- TODO: How SearchServiceVersion enum works. How includeOldApiVersions() customization
+     adds backward-compat versions. Deduplication guard needed. -->
+
+## Post-Regeneration Customizations
+
+<!-- TODO: Document each customization method in SearchCustomizations.java:
+     - hideGeneratedSearchApis
+     - addSearchAudienceScopeHandling
+     - includeOldApiVersions
+     - removeGetApis
+     - hideWithResponseBinaryDataApis (the most fragile one) -->
+
+## Testing Notes
+
+<!-- TODO: How to run tests, recorded test setup with assets.json,
+     environment requirements for live tests. -->
+
+## References
+
+| File | Contents |
+|------|----------|
+| [references/architecture.md](references/architecture.md) | Source layout, package map, dependencies |
+| [references/customizations.md](references/customizations.md) | JavaParser AST patterns, per-customization update guidance |

sdk/search/azure-search-documents/.github/skills/search-documents/references/architecture.md

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+# azure-search-documents SDK Architecture
+
+<!-- TODO: Document the full source layout, generated vs custom split,
+     package map, service version rules, and dependency information. -->

sdk/search/azure-search-documents/.github/skills/search-documents/references/customizations.md

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+# azure-search-documents — Customization Guide
+
+<!-- TODO: Document JavaParser AST patterns, SearchCustomizations.java methods,
+     per-customization update guidance, and common customization patterns. -->