Document and test sarif_list_rules per-rule resultCount field (#219)

* Initial plan

* Enhance sarif_list_rules tests for per-rule resultCount coverage

- Add second sql-injection result to test fixture for varied counts
- Verify resultCount for all rules (not just the first)
- Add test for rules with zero results (resultCount: 0)
- Update related test assertions for the enriched fixture

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* Extract zero-results SARIF fixture into helper function

Address code review feedback: extract inline SARIF object into
createZeroResultsSarif() helper for consistency with existing patterns.

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* Add sarif_list_rules response format documentation to server-tools.md

Document the per-rule resultCount field and complete response schema
in the MCP resource file served to LLMs at runtime. Includes JSON
example, top-level field descriptions, and per-rule field reference
with types and required/optional markers.

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* Polish resultCount description in server-tools.md response table

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* Sync package-lock.json & server/dist/**

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: data-douser <70299490+data-douser@users.noreply.github.com>
Co-authored-by: Nathan Randall <data-douser@github.com>

Author: Copilot