chore: complete the RC.2 public preview release

[terrizoaguimor]

Summary

• add structured bug and feature request templates
• add the repository pull request contract
• align the repository security policy with the live trust center
• harden native watch debouncing after hosted Linux exposed a transient truncate/write snapshot
• reserve this release branch for final crates.io replay evidence and RC.2 release closure

Current evidence

• public site: https://pliegocss.dev
• public repository: https://github.com/celiumsai/pliegocss
• hosted CI authority: https://github.com/celiumsai/pliegocss/actions/runs/29850566211
• hosted CodeQL authority: https://github.com/celiumsai/pliegocss/actions/runs/29850565624

The immutable v0.1.0-rc.2 tag and prerelease will be created from the final merged commit only after all nineteen crates are visible and a clean Rust 1.85 registry replay passes.