[codex] Dedupe Rust dependency versions

[limityan]

Summary

• Move the workspace dashmap requirement to 6.x so direct BitFun crates align with the russh-sftp graph.
• Use the workspace similar requirement from the CLI crate instead of a separate broad requirement.
• Move relay-server's direct dashmap requirement onto the workspace dependency.

Impact

This removes dashmap v5.5.3 from the Rust dependency graph and keeps the remaining direct similar requirements aligned at the workspace level.

Validation

• Confirmed dashmap@5.5.3 is no longer present in cargo tree --workspace --target all.
• Ran cargo check --workspace successfully. The only warning observed was the existing desktop dead-code warning for parse_clipboard_path_segments.

[limityan]

Closing this split PR because the dependency dedupe and modernization commits have been consolidated into #954.