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>

docs/TROUBLESHOOTING.md

@@ -0,0 +1,41 @@
+# Troubleshooting (draft)
+
+> Placeholder. Will be filled in as real failure modes are observed post-MVP.
+> Cross-reference [ARCHITECTURE.md, section 16 (Fehlerbehandlung)](ARCHITECTURE.md#16-fehlerbehandlung)
+> for the error-handling design these entries should map to.
+
+## How to gather diagnostics
+
+```sh
+rc.podman status
+podman info
+podman system df
+```
+
+Relevant log locations:
+
+- Container logs: `/mnt/*/system/podman/logs/containers/`
+- Service log: `/mnt/*/system/podman/logs/podman-service.log`
+- Unraid System Log: `Tools → System Log` in the WebUI
+
+Please redact registry credentials/tokens before sharing logs in an issue.
+
+## Known problem categories (to be populated)
+
+### Storage
+
+- `podman.img` full / near-full
+- Loopback mount failures after unclean shutdown
+
+### Networking
+
+- Custom network / macvlan issues
+- Conflicts with Docker's `iptables` chains
+
+### Autostart
+
+- Container stuck in a failed autostart loop
+
+### Plugin update / rollback
+
+- Config migration failures after an update