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>

packages/containers-common/containers-common.SlackBuild

@@ -0,0 +1,33 @@
+#!/bin/sh
+# SlackBuild for containers-common — unraid-podman
+#
+# Builds a Slackware-compatible .txz package for containers-common, pinned to a specific
+# upstream release from https://github.com/containers/common.
+# See docs/ARCHITECTURE.md section 5 (Paketmanagement) and packages/README.md.
+#
+# STATUS: placeholder — not yet implemented.
+
+set -eu
+
+PRGNAM=containers-common
+VERSION=${VERSION:-0.0.0}   # TODO: pin exact upstream version
+ARCH=${ARCH:-x86_64}
+BUILD=${BUILD:-1}
+TAG=${TAG:-_unraidpodman}
+
+CWD=$(pwd)
+TMP=${TMP:-/tmp/SBo}
+PKG=$TMP/package-$PRGNAM
+OUTPUT=${OUTPUT:-/tmp}
+
+# TODO:
+#   1. Fetch source tarball for $PRGNAM $VERSION from
+#      https://github.com/containers/common
+#   2. Apply patches from packages/containers-common/patches/, if any
+#   3. Build (Go build for Go-based components, make for C-based components)
+#   4. Install into $PKG following Slackware package filesystem layout
+#   5. Copy packages/containers-common/slack-desc into $PKG/install/slack-desc
+#   6. makepkg to produce $OUTPUT/$PRGNAM-$VERSION-$ARCH-$BUILD$TAG.txz
+
+echo "TODO: implement containers-common.SlackBuild"
+exit 1