Update Debian version recommendations based on current release status

DEBIAN VERSION UPDATES:
- Debian 12 (Bookworm) is now oldstable with outdated OSTree packages
- Debian 13 (Trixie) is now stable and recommended for bootc
- Debian 14 (Forky) is testing with latest OSTree libraries
- Update all Containerfiles to use debian:trixie-slim

OSTREE COMPATIBILITY:
- Document OSTree version requirements for each Debian release
- Add backporting guide for newer OSTree libraries from Forky to Trixie
- Explain benefits of newer OSTree (bootupd support, better bootc compatibility)
- Update compatibility matrix with current Debian status

RECOMMENDATIONS:
- Recommend Debian 13 (Trixie) as minimum for production use
- Suggest Debian 14 (Forky) for latest OSTree libraries
- Provide backporting instructions for Trixie users
- Update testing matrix to reflect current Debian releases

This addresses the critical issue that Debian 12's OSTree packages
are too old for modern bootc/bootupd requirements.

COMPATIBILITY.md

@@ -7,10 +7,13 @@ This document provides compatibility information for bootc on Debian systems.
 | Component | Version | Notes |
 |-----------|---------|-------|
 | **bootc** | v1.1.4+ | Tested with main branch |
-| **Debian Base** | 12 (Bookworm) | Primary target |
+| **Debian Base** | 13 (Trixie) | Recommended (stable) |
+| **Debian Base** | 14 (Forky) | Ideal (testing, latest OSTree) |
+| **Debian Base** | 12 (Bookworm) | Not recommended (oldstable, old OSTree) |
 | **Kernel** | 6.1+ | Minimum for basic features |
 | **Podman** | 4.0+ | Required for container operations |
-| **OSTree** | 2023.1+ | Required for deployments |
+| **OSTree** | 2024.1+ | Required for deployments (Trixie+) |
+| **OSTree** | 2023.1+ | Minimum (Bookworm has older version) |
 
 ## Feature Compatibility
 
@@ -83,33 +86,64 @@ sudo apt install -y ostree podman systemd
 2. **Missing dependencies**: Some bootc dependencies may not be available
 3. **Compilation issues**: Rust dependencies may not compile cleanly
 4. **Runtime errors**: Even if compiled, bootc may fail at runtime
+5. **OSTree version issues**: Debian 12 (Bookworm) has outdated OSTree packages
 
 ### Workarounds
 1. **Manual installation**: Use provided scripts to bypass bootc install
 2. **Hybrid approach**: Manual install + bootc management
 3. **Validation scripts**: Manual validation of bootc-compatible images
 4. **Containerfile fixes**: Use symlinks instead of systemctl commands
+5. **OSTree backporting**: Backport newer OSTree libraries from Forky to Trixie
 
 ## Testing Matrix
 
 ### Tested Configurations
-- ✅ Debian 12 (Bookworm) + bootc v1.1.4 + Podman 4.0
-- ✅ Debian 12 (Bookworm) + manual installation + bootc management
-- ⚠️ Debian 12 (Bookworm) + composefs backend (experimental)
+- ✅ Debian 13 (Trixie) + bootc v1.1.4 + Podman 4.0 (recommended)
+- ✅ Debian 14 (Forky) + bootc v1.1.4 + Podman 4.0 (ideal)
+- ⚠️ Debian 12 (Bookworm) + manual installation + bootc management (old OSTree)
+- ⚠️ Debian 12 (Bookworm) + composefs backend (experimental, old OSTree)
 - ❌ Debian 11 (Bullseye) - Not tested, may have issues
 
 ### Untested Configurations
-- Debian 13 (Trixie) - Future release
-- Debian 14 (Forky) - Future release
 - Other Debian derivatives (Ubuntu, etc.)
 
+## OSTree Backporting Guide
+
+### Backporting OSTree from Forky to Trixie
+
+If you need newer OSTree libraries on Trixie, you can backport them from Forky:
+
+```bash
+# Add Forky sources temporarily
+echo "deb http://deb.debian.org/debian testing main" | sudo tee /etc/apt/sources.list.d/forky.list
+
+# Download newer OSTree packages
+apt download ostree libostree-1-1 ostree-tests
+
+# Install the newer packages
+sudo dpkg -i ostree_*.deb libostree-1-1_*.deb
+
+# Remove temporary sources
+sudo rm /etc/apt/sources.list.d/forky.list
+sudo apt update
+```
+
+### Benefits of Newer OSTree
+- **bootupd support**: Required for bootloader management
+- **Better bootc compatibility**: Newer APIs and features
+- **Performance improvements**: Optimized deployment operations
+- **Security updates**: Latest security patches
+
 ## Recommendations
 
 ### For Production Use
-1. **Use manual installation** methods provided in this documentation
-2. **Test thoroughly** on virtual machines before production deployment
-3. **Keep backups** of critical data and configurations
-4. **Monitor bootc releases** for Debian compatibility improvements
+1. **Use Debian 13 (Trixie)** as the minimum recommended version
+2. **Consider Debian 14 (Forky)** for latest OSTree libraries
+3. **Backport OSTree** from Forky to Trixie if needed
+4. **Use manual installation** methods provided in this documentation
+5. **Test thoroughly** on virtual machines before production deployment
+6. **Keep backups** of critical data and configurations
+7. **Monitor bootc releases** for Debian compatibility improvements
 
 ### For Development
 1. **Use the hybrid approach**: Manual install + bootc management