ci: add security workflows (CodeQL, Scorecard, Dependabot)

[imran-siddique]

Adds baseline security tooling to match cmcp/ca2a/agent-manifest: CodeQL (SAST), OSSF Scorecard, and Dependabot config, plus CODEOWNERS/LICENSE where missing. Ref: internal security hardening bundle (agentrust-io Appendix B).

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