chore(ci): enforce cargo deny via reusable action

[RAprogramm]

Summary

• add a composite GitHub Action that installs cargo-deny and hook it into the reusable CI workflow
• surface the cargo-deny job status in the README badges and document the change
• bump the crate to v0.5.1 and record the release in the changelog

Testing

• cargo +nightly fmt --all
• cargo build --all-targets
• cargo test --all
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo doc --no-deps

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https://chatgpt.com/codex/tasks/task_e_68ccc18fb74c832bbd0b548ee502f9a3