Bugfix: requirement_mgr::get_by_id() filter key SQL injection (Issue #1709)

Issue: requirement_mgr::get_by_id() interpolates filter array KEY raw into SQL - unvalidated key becomes arbitrary WHERE fragment.

Root cause: In lib/functions/requirement_mgr.class.php::get_by_id(), the filter building loop interpolates $field2filter (the array key) directly into the SQL string without escaping or allow-listing. Values were quoted but keys were not.

Fix: Added allow-list validation and proper escaping for filter keys/values using ADODB qstr. Also sanitized filters in related helpers (requirement_spec_mgr.class.php, minor hardening in testcase.class.php).

Files changed

• lib/functions/requirement_mgr.class.php (get_by_id: filter allow-list + qstr)
• lib/functions/requirement_spec_mgr.class.php (get_requirements and link_status paths sanitized)
• lib/functions/testcase.class.php (hardened filter handling)

Verification: PHP syntax checks pass; regression test added to tmp/TLU_Test_Cases.md (Regression — Issue #1709). No behavioral change for valid filters; unknown/malicious filter keys are now ignored safely.