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>

.github/workflows/lint.yml

@@ -0,0 +1,53 @@
+name: Lint
+
+# Static analysis over shell scripts (ShellCheck) and the .plg/XML manifest
+# (xmllint) on every push and pull request. Mirrors scripts/dev/lint.sh for
+# local use.
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  shellcheck:
+    name: ShellCheck
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install ShellCheck
+        run: |
+          sudo apt-get update -qq
+          sudo apt-get install -y --no-install-recommends shellcheck
+
+      - name: Run ShellCheck
+        run: |
+          set -eu
+          # shellcheck disable=SC2038  (find | xargs is fine here, filenames
+          # in this repo never contain spaces/newlines)
+          find plugin/rc.d plugin/sbin scripts -type f \
+            \( -name '*.sh' -o -name 'rc.*' -o -name '*.SlackBuild' \) \
+            -print0 \
+          | xargs -0 shellcheck --severity=warning --external-sources
+
+  xmllint:
+    name: Validate .plg XML
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install libxml2-utils
+        run: |
+          sudo apt-get update -qq
+          sudo apt-get install -y --no-install-recommends libxml2-utils
+
+      - name: Validate podman.plg is well-formed XML
+        run: xmllint --noout plugin/podman.plg
+
+  editorconfig:
+    name: EditorConfig
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: editorconfig-checker/action-editorconfig-checker@main