feat: manage Rust quality policy through repository

[rozsazoltan]

Summary

Adds a repository-managed Rust quality policy that can be shared across projects while still allowing project-specific extensions.

Changes

• Add Rust quality policy settings to datarose.toml.
• Generate and update Cargo lint configuration from verzly repository.
• Add default [workspace.lints.rust] and [workspace.lints.clippy] policy for Rust workspaces.
• Add [lints] workspace = true to workspace member crates.
• Generate .clippy.toml as the shared Clippy threshold/config file.
• Keep .clippy.toml focused on Clippy configuration values instead of lint policy.
• Validate the new quality.rust schema surface in repository check.
• Make repository check detect missing Rust lint defaults and missing .clippy.toml.
• Document the repository-managed Rust quality model in the README.

Notes

The default policy is intentionally portable: it forbids unsafe code, denies unused must_use results, denies the standard Clippy lint set, and blocks obvious development leftovers such as dbg!, todo!, and unimplemented!.

Projects can extend or override the policy through datarose.toml, then apply it with verzly repository update.