Add reproducible build system, native Unraid plugin, and WebUI

- versions.env pins podman, conmon, crun, netavark, aardvark-dns, passt,
  and fuse-overlayfs to verified upstream source checksums; SlackBuild
  recipes, scripts/build-packages.sh, checksums.sh, release.sh, and
  update-versions.sh implement the reproducible pipeline; GitHub Actions
  workflows build in a Slackware container and publish releases without
  committing any binaries.

- plugin/podman.plg installs/updates/removes all eight packages (the
  seven components plus the plugin's own unraid-podman scaffolding
  package) via upgradepkg, using the official Unraid array-event hook
  mechanism (event/disks_mounted, event/stopping) instead of editing
  /boot/config/go. rc.podman and the sbin/ helper scripts implement
  storage creation, config seeding/sync, preflight checks, autostart
  with per-container Safe-Mode, and package verify/update/rollback.

- webui/plugins/podman implements the Dashboard, Containers, Pods,
  Images, Volumes, Networks, Logs, Terminal, Compose, and Settings
  panels against the approved mockup (webui/mockups/prototype.html),
  talking to podman system service exclusively via PodmanClient.php
  (libpod REST API over the Unix socket), with two documented
  exceptions: Terminal's one-shot exec model and Compose's use of the
  podman compose CLI, since libpod has no REST equivalent for either.

- docs/ARCHITECTURE.md and docs/ROADMAP.md record the design decisions
  and honest current status (syntax-checked, unit- and
  integration-tested against fake sockets/servers; not yet run against
  a real Unraid/Podman/Slackware system).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

config/storage.conf

@@ -0,0 +1,21 @@
+# Default storage.conf template for unraid-podman.
+#
+# Defines the Podman storage graph root/driver. On Unraid this MUST point at
+# the mounted podman.img loopback (or equivalent cache-pool/disk path), never
+# at a path under /mnt/user (FUSE) or RAM-root /var/lib/containers directly.
+# See docs/ARCHITECTURE.md section 4.3 and section 10 (Images).
+#
+# Full reference: https://github.com/containers/storage/blob/main/docs/containers-storage.conf.5.md
+
+[storage]
+driver = "overlay"
+# runroot and graphroot are set at runtime by rc.podman based on
+# /boot/config/plugins/podman/podman.cfg (configurable storage location),
+# not hardcoded here. TODO: document the exact substitution mechanism once
+# rc.podman is implemented.
+# graphroot = "/var/lib/containers/storage"
+# runroot = "/var/run/containers/storage"
+
+[storage.options]
+# TODO: overlay-specific mount options once the loopback filesystem
+# (XFS with ftype=1, or BTRFS) is finalized.