[Security] Secure coding baseline for Symfony/PHP service

[sdntsng]

objective

establish secure coding and dependency hygiene baseline for the php/symfony service.

scope

• input validation + output encoding checklist
• authn/authz placeholders for protected routes
• dependency audit workflow (composer + github advisories)
• secret handling guidance for local/prod

acceptance criteria

• security checklist documented and applied to core endpoints
• automated dependency scan wired in ci
• no known critical vulnerabilities in default branch

resume evidence

can be cited as secure coding + vulnerability prevention work.