feat: Add comprehensive Linux packaging and deployment documentation for CommDesk

- Introduced FLATPAK_BUILD_GUIDE.md for Flatpak packaging instructions.
- Created FLATPAK_COMMANDS.sh for quick reference commands related to Flatpak.
- Developed PRODUCTION_DEPLOYMENT.md outlining production deployment strategies and CI/CD workflows.
- Established TESTING_AND_QA.md detailing testing architecture, QA workflows, and performance validation.
- Added latest.json for version management and release notes.
- Created org.commdesk.CommDesk.desktop for application integration.
- Included release.pub for update signing with Minisign public key.

Co-authored-by: Copilot <copilot@github.com>

Author: abhishek-nexgen-dev