Add agent dev skill for search

[xiangyan99]

Description

Add an agent dev skill for the search-documents package

Please add an informative description that covers that changes made by the pull request and link all relevant issues.

If an SDK is being regenerated based on a new API spec, a link to the pull request containing these API spec changes should be included above.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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• Title of the pull request is clear and informative.
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Testing Guidelines

• Pull request includes test coverage for the included changes.

[Copilot]

Pull request overview

Adds a package-specific “agent dev skill” for azure-search-documents to guide post-TypeSpec-regeneration validation and re-application of hand-authored _patch.py customizations, and registers it in the repo-wide package skill registry.

Changes:

• Added a search-documents skill (SKILL.md) describing regeneration verification steps and customization patterns.
• Added a references/customizations.md inventory of _patch.py customizations and their generated-code dependencies.
• Updated the central find-package-skill registry to include azure-search-documents.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
sdk/search/azure-search-documents/.github/skills/search-documents/references/customizations.md	New checklist documenting each customization file’s defined symbols and regeneration verification points.
sdk/search/azure-search-documents/.github/skills/search-documents/SKILL.md	New skill guide for post-tsp-client update regeneration verification and customization re-checks.
.github/skills/find-package-skill/SKILL.md	Registers the azure-search-documents package skill in the central skill lookup table.

[mccoyp]

Can we move these skill files to the root .github/ folder? We're aiming for a pattern where service-specific skills are at azure-sdk-for-python/.github/skills/<service> -- for example, https://github.com/Azure/azure-sdk-for-python/tree/main/.github/skills/ml