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>

webui/plugins/podman/ajax/images.php

@@ -0,0 +1,88 @@
+<?php
+/**
+ * ajax/images.php
+ *
+ * Backs the Images panel.
+ *
+ * Actions (?action=...):
+ *   list     GET  -> normalized image list
+ *   pull     POST {"reference": "docker.io/library/postgres:16"}
+ *   remove   POST {"id": "...", "force": false}
+ */
+
+declare(strict_types=1);
+
+require __DIR__ . '/../include/bootstrap.php';
+
+$action = $_GET['action'] ?? '';
+
+switch ($action) {
+    case 'list':
+        podman_json_response(images_list($client));
+        break;
+
+    case 'pull':
+        $body = podman_read_json_body();
+        $reference = (string) ($body['reference'] ?? '');
+        if ($reference === '') {
+            podman_json_error('Missing reference in request body', 400);
+        }
+        podman_json_response($client->pullImage($reference));
+        break;
+
+    case 'remove':
+        $body = podman_read_json_body();
+        $id = (string) ($body['id'] ?? '');
+        if ($id === '') {
+            podman_json_error('Missing id in request body', 400);
+        }
+        $client->removeImage($id, (bool) ($body['force'] ?? false));
+        podman_json_response(['status' => 'removed']);
+        break;
+
+    default:
+        podman_json_error("Unknown action '{$action}'", 400);
+}
+
+/** @return array<int,array<string,mixed>> */
+function images_list(PodmanClient $client): array
+{
+    $raw = $client->listImages();
+
+    // In-use counts let the frontend show "0" (safe to remove) vs a
+    // positive count, without a separate round trip per image.
+    $usageCounts = [];
+    foreach ($client->listContainers(true) as $c) {
+        $imageId = (string) ($c['ImageID'] ?? '');
+        if ($imageId !== '') {
+            $usageCounts[$imageId] = ($usageCounts[$imageId] ?? 0) + 1;
+        }
+    }
+
+    $out = [];
+    foreach ($raw as $img) {
+        $id = (string) ($img['Id'] ?? '');
+        $repoTags = $img['RepoTags'] ?? [];
+        $repository = '<none>';
+        $tag = '<none>';
+        if (is_array($repoTags) && count($repoTags) > 0 && is_string($repoTags[0]) && str_contains($repoTags[0], ':')) {
+            [$repository, $tag] = explode(':', $repoTags[0], 2);
+        }
+
+        $out[] = [
+            'id' => $id,
+            'shortId' => podman_short_id($id),
+            'repository' => $repository,
+            'tag' => $tag,
+            'sizeBytes' => (int) ($img['Size'] ?? 0),
+            'sizeFormatted' => podman_format_bytes((int) ($img['Size'] ?? 0)),
+            // Unlike containers' Created/StartedAt (RFC3339 strings), libpod
+            // reports image Created as a Unix timestamp integer directly.
+            'createdAt' => isset($img['Created']) ? (int) $img['Created'] : null,
+            'usedBy' => $usageCounts[$id] ?? 0,
+        ];
+    }
+
+    usort($out, static fn($a, $b) => strcmp($a['repository'], $b['repository']));
+    return $out;
+}