docs: add missing CI/CD workflow entries to deployment documentation

[VerifiedFlemzy1]

Closes #477
This PR updates the deployment documentation to accurately reflect all CI/CD workflows in the repository.

What was fixed

The CI/CD pipeline table in docs/DEPLOYMENT.md originally listed only three workflows (ci.yml, release.yml, deploy.yml). The repository actually contains five active workflow files:

• load-test.yml – scheduled k6 load‑testing scenarios (and can be triggered manually)
• security-audit.yml – scheduled security audits (dependency audit, code scan, secret detection, license compliance) and can also be run manually

Changes

• Added rows for load-test.yml and security-audit.yml to the CI/CD pipeline table, including their triggers and a concise description of what each workflow does.
• Updated the table header to list all five workflows.

No other files were modified.

Why this matters

Keeping the documentation in sync with the actual CI configuration prevents confusion for contributors and ensures that the CI/CD pipeline overview is complete and reliable.

Verification

The updated table now renders correctly in the Markdown preview and matches the files present in .github/workflows/.

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Open the PR:
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https://github.com/VerifiedFlemzy1/backend/pull/new/fix-deployment-ci-doc

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