Validate search query input

[bozicovichsantiago20-oss]

Summary

• Add a search query validator for GET /api/search.
• Default missing q to an empty string, trim valid string input, and cap q at 200 characters.
• Reject non-string query input such as repeated q parameters with a structured 400 response.
• Add focused API tests and update the package test script to run test files.

Verification

• npm.cmd test -w apps/api
• node --test apps/api/src/tests/search.test.js
• git diff --check

Closes #4191
Refs #743
/claim #4191