Fix real STORAGE_PATH bug; add Start Podman + format-disk from the WebUI

Root cause of a fresh-install "cannot reach the Podman API socket" report
(a friend's Unraid box, cache pool present and mounted): unlike
Docker-for-Unraid's docker.img path, this plugin never auto-created
STORAGE_PATH itself — only podman.img inside it. A perfectly normal,
already-mounted cache pool still failed preflight/storage-create with
"does not exist", just because its own .../system/podman subdirectory
had never been created. Fixed by walking up to the nearest existing
ancestor and checking whether it's on a different device than / (real
mount vs. nothing mounted at all) — see podman-common.sh's new
podman_path_has_real_mount_ancestor(), used by both podman-preflight.sh
and podman-storage.sh.

Settings gets a "Podman Service" card (status chip + Start/Restart,
backed by new ajax/settings.php service_status/start/restart actions
that just shell out to rc.podman) so a fresh install that failed to start
can be diagnosed and retried without SSH/terminal access at all — exactly
what was missing when this was first needed live.

Also adds "Format a Disk for Podman Storage" (new ajax/disks.php) for a
single-disk system with no cache pool at all. Only ever lists disks with
literally no existing partition/filesystem/RAID-or-ZFS-membership
signature and that aren't Unraid's boot flash — found live, twice, during
development: the boot USB (FAT, labeled "UNRAID") passed the initial
mounted-only check because this host's /boot is backed by a ZFS dataset
rather than a direct partition mount, and active RAID-member cache disks
passed a data-vs-blank *warning* rather than a hard exclusion. Both are
now excluded outright, not just flagged — see disks.php's
device_or_children_labeled_unraid() and the hasData exclusion in
list_candidate_disks(). A disk formatted this way is remounted by UUID on
every boot via a new plugin/sbin/podman-mount-managed-disk.sh, called
from plugin/event/disks_mounted before rc.podman start.

Unrelated fix bundled in: scripts/lib/slackbuild-common.sh now sets
SOURCE_DATE_EPOCH (derived from the repo's last commit) before calling
makepkg, so two separate builds of the same commit produce byte-identical
.txz files — makepkg already supports this (`--clamp-mtime` when
$SOURCE_DATE_EPOCH is set, confirmed by reading a real host's
/sbin/makepkg) but nothing was setting the variable, so release.yml's
"rebuild in CI and verify it matches the committed checksums" step was
guaranteed to fail on the first package it checked alphabetically
(observed live: aardvark-dns).

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

plugin/sbin/podman-preflight.sh

@@ -75,6 +75,14 @@ elif [ -d "$STORAGE_PATH" ]; then
   else
     fail "STORAGE_PATH ($STORAGE_PATH) does not appear to be on a mounted filesystem"
   fi
+elif podman_path_has_real_mount_ancestor "$STORAGE_PATH"; then
+  # The leaf directory doesn't exist yet, but a real filesystem IS mounted
+  # somewhere along its path (e.g. the cache pool itself) — podman-storage.sh
+  # create will mkdir -p it. Not a failure; see that check's own comment
+  # for the live bug this used to cause (a normal, already-mounted cache
+  # pool failing preflight just because its .../system/podman subdirectory
+  # had never been created).
+  ok "STORAGE_PATH ($STORAGE_PATH) doesn't exist yet, but resolves onto a mounted filesystem — will be created"
 else
   fail "STORAGE_PATH ($STORAGE_PATH) does not exist — is the configured cache pool/disk present and started?"
 fi