fix(config): validate protected cookie stores

[iMelki]

Summary

• Validate configuration through the same secure-file reader used by the application.
• Accept Windows DPAPI-protected manual-cookie stores without converting them to plaintext.
• Add focused coverage for a valid protected store and malformed-wrapper error redaction.

Validation

• git diff --check
• cargo fmt --all --check
• gitleaks protect --staged --redact
• Focused Rust test compilation is currently blocked locally before tests start: Cargo returns Windows os error 2 while copying the num-traits build script. The failed build cache and logs were preserved; no security product or source data was changed.
• The upstream PR check workflow is awaiting maintainer approval because this is a first-time fork contribution.

Privacy

This change does not include account cookies, credential values, personal paths, or local configuration data.

[Finesssee]

Thanks for the PR, I will review it ASAP.