Add Proxmox VE 8 image support

Debian 12 Bookworm base with Proxmox VE 8.4 (pve-manager, pve-qemu-kvm,
qemu-server). Headless hypervisor managed via web UI at https://<ip>:8006.
Login: root/proxmox.

The PS5 kernel can't satisfy proxmox-ve's hard dependency on a Proxmox
kernel, so the recipe installs an equivs stub (ps5-proxmox-kernel-stub)
that Provides: proxmox-default-kernel before installing proxmox-ve. First
boot auto-bridges the PS5 ethernet into vmbr0 with DHCP. WiFi is not
included (Proxmox VM networking requires wired bridging).

Also wires proxmox into the CI matrix, entrypoint staging, and release
table.

[skip ci]

.github/workflows/build-image.yml

@@ -8,7 +8,7 @@ on:
         description: 'Distribution'
         default: 'ubuntu2604'
         type: choice
-        options: [all, ubuntu2604, arch, cachyos, kali, fedora]
+        options: [all, ubuntu2604, arch, cachyos, kali, fedora, proxmox]
   workflow_call:
     inputs:
       distro:
@@ -34,7 +34,7 @@ jobs:
         run: |
           INPUT="${{ inputs.distro || 'ubuntu2604' }}"
           if [ "$INPUT" = "all" ]; then
-            echo 'distros=["kali","ubuntu2604","arch","cachyos","fedora"]' >> "$GITHUB_OUTPUT"
+            echo 'distros=["kali","ubuntu2604","arch","cachyos","fedora","proxmox"]' >> "$GITHUB_OUTPUT"
           else
             echo "distros=[\"$INPUT\"]" >> "$GITHUB_OUTPUT"
           fi
@@ -164,6 +164,9 @@ jobs:
             if [ -f meta/fedora.sha256 ]; then
               echo "| Fedora 44 | [\`ps5-fedora.img.xz\`](https://pub-561df4012f1a46fbbdf618d5cc5941f6.r2.dev/ps5-fedora.img.xz) |"
             fi
+            if [ -f meta/proxmox.sha256 ]; then
+              echo "| Proxmox VE 8 | [\`ps5-proxmox.img.xz\`](https://pub-561df4012f1a46fbbdf618d5cc5941f6.r2.dev/ps5-proxmox.img.xz) |"
+            fi
             echo ""
             echo "**SHA256 checksums:**"
             echo "\`\`\`"