Fix five real bugs found by actually installing and running the plugin

First live end-to-end install on real Unraid hardware (all 8 built
packages installed via upgradepkg, rc.podman started, containers
pulled/run/networked/port-mapped) — surfaced five genuine bugs no
amount of container-based CI testing could have caught, since none of
them exist inside the vbatts/slackware:15.0 build container:

1. rc.podman never created $PODMAN_LOG_DIR before redirecting the
   podman system service's output into it, so the service failed to
   even start ("No such file or directory"). Added it alongside the
   existing PODMAN_RUN_DIR mkdir.

2. config/storage.conf hardcoded a [storage] table, and
   podman-config.sh's `sync` step appended a second one at boot with
   the real graphroot/runroot — TOML forbids defining the same table
   twice. Removed the template's [storage] entirely; sync already
   generates the whole thing.

3. config/policy.json had a "_comment" pseudo-field for
   documentation, but containers/image's policy parser rejects any
   unknown top-level key outright. JSON has no comment syntax; moved
   the rationale into docs/ARCHITECTURE.md instead.

4. netavark >= 2.0 dropped its iptables firewall driver entirely
   (verified: passing "iptables" is flatly rejected) — nftables or
   firewalld are the only remaining options, and firewalld needs
   systemd/dbus, which Unraid has neither of. Set firewall_driver =
   "nftables" explicitly and documented that Unraid OS doesn't ship
   the `nft` binary this needs (a slackware64 nftables package works;
   not yet wired into the build/install pipeline — see follow-up).

5. Every container failed with "crun: pivot_root: Invalid argument".
   Root cause: Unraid's / is permanently the kernel's initial "rootfs"
   pseudo-filesystem (Unraid never pivots to a real one at boot — the
   whole OS runs from RAM), and pivot_root(2) unconditionally rejects
   that as the old root. This is not new: Docker/runc hits the exact
   same kernel restriction on this exact host and silently falls back
   to an MS_MOVE-based chroot; crun has no such fallback, only a
   --no-pivot flag with no config-file equivalent. Added
   plugin/sbin/crun-no-pivot.sh, a thin wrapper that scans crun's full
   argument list (podman puts global flags before the subcommand, so
   the subcommand isn't reliably $1) and injects --no-pivot right
   after create/run, and pointed containers.conf's crun runtime at it.
   Also fixed the podman.plg postinstall's chmod glob
   (`podman-*.sh` -> `*.sh`), which would have skipped this new
   non-podman-prefixed sbin script.

Verified end-to-end on the real host: pull, run, real network
connectivity (wget through the container's bridge), and a published
port actually serving HTTP (curl through -p 8099:80 to nginx) all
work. --no-pivot's security tradeoff (disabling one particular
container-escape mitigation) was explicitly discussed with and
approved by the user before committing, given it must be the default
for any container to start at all on this platform.

Follow-up not yet done: nftables (needed for #4) is not yet a
packages/ component in the reproducible build pipeline — it was only
installed manually on the test host for this verification run.

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

plugin/sbin/crun-no-pivot.sh

@@ -0,0 +1,37 @@
+#!/bin/bash
+# =============================================================================
+# plugin/sbin/crun-no-pivot.sh
+#
+# Thin OCI-runtime wrapper around crun, injecting --no-pivot on `create`/
+# `run`. Unraid's / is the kernel's initial "rootfs" pseudo-filesystem —
+# Unraid never pivots to a real one during boot, the whole OS runs from
+# RAM — and pivot_root(2) unconditionally rejects that as the "old root"
+# (EINVAL). runc (what Docker uses) silently falls back to an MS_MOVE-based
+# chroot in that situation; crun has no such fallback and no config-file
+# equivalent, only this per-invocation flag — so config/containers.conf
+# points podman's crun runtime at this wrapper instead of crun directly.
+# See docs/ARCHITECTURE.md section 8.
+#
+# Verified live: without this, every container fails with
+# "crun: pivot_root: Invalid argument: OCI runtime error".
+#
+# --no-pivot is only a valid flag on crun's create/run subcommands (see
+# `crun run --help`) — every other subcommand (delete, exec, kill, list,
+# ...) is passed straight through unmodified. podman invokes crun with its
+# own global flags BEFORE the subcommand (e.g.
+# `crun --log-format=json --log <path> create --bundle <path> ...`), so
+# the subcommand is not reliably $1 — scan every argument instead of only
+# checking the first one, and insert --no-pivot immediately after
+# create/run wherever it actually appears.
+# =============================================================================
+
+args=()
+found=0
+for arg in "$@"; do
+  args+=("$arg")
+  if [ "$found" -eq 0 ] && { [ "$arg" = create ] || [ "$arg" = run ]; }; then
+    args+=("--no-pivot")
+    found=1
+  fi
+done
+exec /usr/bin/crun "${args[@]}"