docs: add security architecture diagrams for boundary and github actions (#58)

* Initial plan

* docs: add security architecture page with mermaid diagrams

Co-authored-by: Mossaka <[email protected]>

* docs: address code review feedback on security architecture

Co-authored-by: Mossaka <[email protected]>

* docs: clarify why --keep-containers should not be used in ci

Co-authored-by: Mossaka <[email protected]>

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Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: Mossaka <[email protected]>

Author: Copilot