improve: enhance rootfs command robustness and flexibility

- Remove dependency on manifest parsing for reference discovery
- Automatically detect and use first available OSTree reference
- Simplify command usage - no need to parse treefile for reference name
- Add better error handling for empty repositories
- Improve user experience by showing which reference is being used
- Make command more flexible for different use cases

minimal-treefile-with-kernel.yaml

@@ -0,0 +1,83 @@
+api_version: "1.0"
+kind: "tree"
+metadata:
+  ref_name: "test/minimal"
+  version: "0.1.0"
+  description: "Minimal test tree for bootc image generation"
+repositories:
+  - name: "debian"
+    url: "http://deb.debian.org/debian"
+    suite: "trixie"
+    components: ["main"]
+    enabled: true
+packages:
+  base: ["bash", "coreutils", "grep", "gawk", "sed", "linux-image-amd64", "linux-headers-amd64"]
+  additional: []
+  excludes: []
+output:
+  generate_container: true
+  container_path: "/tmp/apt-ostree-container"
+  export_formats:
+    - "docker-archive"
+    - "oci"
+system:
+  # Create required bootc directories
+  directories:
+    - "/sysroot"
+    - "/usr/lib/bootc"
+    - "/usr/lib/ostree"
+    - "/usr/lib/systemd/system-preset"
+  
+  # Enable required systemd services
+  services:
+    - "systemd-networkd"
+    - "systemd-resolved"
+    - "systemd-sysusers"
+    - "systemd-tmpfiles-setup"
+  
+  # Create composefs configuration
+  files:
+    - path: "/usr/lib/ostree/prepare-root.conf"
+      content: |
+        [prepare-root]
+        composefs=1
+        composefs-store=/ostree/repo
+      mode: "0644"
+      owner: "root:root"
+    
+    - path: "/usr/lib/bootc/install/00-debian.toml"
+      content: |
+        [install]
+        filesystem = "ext4"
+        root-fs-type = "ext4"
+        
+        [install.kernel-args]
+        default = ["console=ttyS0,115200", "quiet"]
+      mode: "0644"
+      owner: "root:root"
+    
+    - path: "/usr/lib/systemd/tmpfiles.d/10-bootc.conf"
+      content: |
+        # Bootc required directories
+        d /var/log 0755 root root
+        d /var/cache 0755 root root
+        d /var/tmp 1777 root root
+        d /tmp 1777 root root
+        d /run 0755 root root
+        d /sysroot 0755 root root
+        d /ostree 0755 root root
+        d /boot 0755 root root
+      mode: "0644"
+      owner: "root:root"
+
+# Post-installation cleanup and setup
+postinstall:
+  - "echo 'Setting up bootc-compatible filesystem...'"
+  - "mkdir -p /sysroot /ostree /usr/lib/bootc /usr/lib/ostree"
+  - "echo 'Cleaning up log files for reproducible builds...'"
+  - "find /var/log -type f -name '*.log' -delete"
+  - "find /var/log -type f -name '*.log.*' -delete"
+  - "find /var/cache -type f -delete"
+  - "echo 'Setting up systemd tmpfiles...'"
+  - "systemd-tmpfiles --create --remove"
+  - "echo 'Bootc setup completed successfully'"