Add ModSecurity repository analysis of JSON and YAJL usage

[Easton97-Jens]

Motivation

• Provide a repository-only, evidence-backed technical analysis focused on how JSON and YAJL are used across the codebase and tests, and store it as an in-repo artifact for reviewers and maintainers.

Description

• Add a single new file modsecurity_repo_analysis.md at the repository root containing an 8‑part analysis (overview, architecture, build/deps, JSON usage, YAJL usage, concrete code evidence, analysis limits, conclusion) with explicit file-and-symbol citations (e.g., src/request_body_processor/json.cc, src/transaction.cc, test/*, build/yajl.m4, configure.ac, modsecurity.conf-recommended).

Testing

• Verified the analysis file was created and inspected its contents locally; no automated unit/regression tests were executed as part of this change.

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Codex Task