feat: Add multi-version Debian support (Trixie + Forky)

- Added support for Debian 14 (Forky) testing release
- Created examples for both Debian 13 (Trixie) and Debian 14 (Forky)
- Added comprehensive multi-version documentation
- Created automated version switching script with backup/restore
- Updated README with version-specific configuration examples
- Added migration guidance between Debian versions

This enables users to build images for both stable (Trixie) and
testing (Forky) releases with easy switching between versions.

examples/debian-basic.json.backup.20250812_003400

@@ -0,0 +1,91 @@
+{
+  "version": "2",
+  "pipelines": [
+    {
+      "name": "build",
+      "runner": "org.osbuild.linux",
+      "stages": [
+        {
+          "name": "org.osbuild.debian.sources",
+          "options": {
+            "suite": "trixie",
+            "mirror": "https://deb.debian.org/debian",
+            "components": ["main", "contrib", "non-free"],
+            "additional_sources": [
+              "deb https://deb.debian.org/debian-security trixie-security main contrib non-free"
+            ]
+          }
+        },
+        {
+          "name": "org.osbuild.debian.debootstrap",
+          "options": {
+            "suite": "trixie",
+            "mirror": "https://deb.debian.org/debian",
+            "variant": "minbase",
+            "arch": "amd64",
+            "components": ["main", "contrib", "non-free"]
+          }
+        },
+        {
+          "name": "org.osbuild.debian.apt",
+          "options": {
+            "packages": [
+              "sudo",
+              "openssh-server",
+              "systemd-sysv",
+              "curl",
+              "wget",
+              "vim",
+              "less",
+              "locales",
+              "ca-certificates",
+              "tzdata",
+              "net-tools",
+              "iproute2"
+            ],
+            "update": true,
+            "clean": true
+          }
+        },
+        {
+          "name": "org.osbuild.debian.locale",
+          "options": {
+            "language": "en_US.UTF-8",
+            "additional_locales": ["en_GB.UTF-8", "de_DE.UTF-8"],
+            "default_locale": "en_US.UTF-8"
+          }
+        },
+        {
+          "name": "org.osbuild.debian.timezone",
+          "options": {
+            "timezone": "UTC"
+          }
+        },
+        {
+          "name": "org.osbuild.debian.users",
+          "options": {
+            "users": {
+              "debian": {
+                "password": "$6$rounds=656000$salt$hashedpassword",
+                "shell": "/bin/bash",
+                "groups": ["sudo", "users", "adm"],
+                "uid": 1000,
+                "gid": 1000,
+                "home": "/home/debian",
+                "comment": "Debian User"
+              }
+            },
+            "default_shell": "/bin/bash",
+            "default_home": "/home"
+          }
+        }
+      ]
+    }
+  ],
+  "assembler": {
+    "name": "org.osbuild.tar",
+    "options": {
+      "compression": "gzip"
+    }
+  }
+}