Add shared helper for optional integer query params

[aniokedianne]

Closes #272

Summary

• added normalizeOptionalIntegerQueryParam in src/utils/query.utils.ts
• updated safeIntParam to use the helper for trimming and strict integer parsing
• added focused helper tests in src/utils/test/query.utils.test.ts

Scope

• only optional integer query param normalization behavior
• no unrelated endpoint or feature changes

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