chore: Prepare for public release

Public Release Preparation:
- Added CONTRIBUTING.md with contribution guidelines
- Added SECURITY.md with vulnerability reporting process
- Updated README.md with badges and public repository links
- Cleaned internal references (genericized production examples)
- Updated all repository links to PlusOne/dbbackup
- Updated Docker registry to git.uuxo.net/PlusOne/dbbackup

Documentation:
- Contribution guidelines (code style, PR process, testing)
- Security policy (supported versions, disclosure process)
- Community support (issues, discussions, security contact)

Repository Links Updated:
- All git.uuxo.net/uuxo/dbbackup → git.uuxo.net/PlusOne/dbbackup
- Download links, Docker registry, clone URLs updated
- Issue tracker and documentation links updated

Ready for public release! 🚀

CHANGELOG.md

@@ -106,7 +106,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Better error messages for PITR operations
 
 ### Production
-- **Deployed at uuxoi.local**: 2 production hosts
+- **Production Validated**: 2 production hosts
 - **Databases backed up**: 8 databases nightly
 - **Retention policy**: 30-day retention with minimum 5 backups
 - **Backup volume**: ~10MB/night