Add Pod lifecycle management, fix nav registration and context-menu bugs

Pods panel could previously only list pods - there was no way to create
one, start/stop/restart it, or attach a container to it from the UI.
Adds a "New Pod" modal (name + port mappings), a per-pod lifecycle menu
(start/stop/restart/remove), and an optional "Pod" field on the Create
Container modal to join an existing pod's network namespace. Backend
verified live against the real podman socket (/pods/create, /pods/{name}/
restart, container "pod" field).

Also fixes three real bugs found via live testing:
- Podman.page used Menu="Podman" instead of Menu="Tasks:<rank>", so the
  plugin never actually appeared in Unraid's top navigation (traced through
  PageBuilder.php/DefaultPageLayout.php/Navigation/Main.php - only pages
  registered under "Tasks" become top-level tabs).
- app.js's shared context-menu component mis-mapped every item positioned
  after a 'separator' entry to the wrong DOM element (an off-by-one against
  menu.children, which includes the separator <div>s) - so "Remove", which
  always sits after a separator, silently did nothing when clicked. Fixed
  by indexing into querySelectorAll('button') instead.
- That same menu was positioned via "position: absolute" math that assumed
  a viewport-relative containing block, but Unraid's own page wrapper
  (webGui/styles/default-base.css's ".content") sets position:relative,
  so the menu rendered far from its anchor button. Switched to
  "position: fixed" with viewport-relative coordinates.

Incidentally, pods add a hidden "infra" container that was leaking into
the plain Containers list with no working lifecycle of its own (always
"running", so its own Remove was permanently disabled) - now filtered out
via libpod's IsInfra flag. And every action-buttons table cell used
"display: flex" directly on the <td>, which browsers can size
inconsistently row to row - moved onto an inner wrapper div instead, and
bumped .podman-btn-icon's touch target size.

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

webui/plugins/podman/ajax/containers.php

@@ -21,7 +21,7 @@
  *   create    POST {"image": "...", "name": "...", "networkMode": "bridge"|"host"|"none"|"<custom-network-name>",
  *                    "ports": [{"hostPort": 8080, "containerPort": 80, "protocol": "tcp"}],
  *                    "volumes": [{"kind": "named"|"path", "source": "myvol"|"/mnt/...", "containerPath": "/data"}],
- *                    "env": [{"key": "...", "value": "..."}], "restartPolicy": "no",
+ *                    "env": [{"key": "...", "value": "..."}], "restartPolicy": "no", "pod": "<existing-pod-name>",
  *                    "privileged": false, "startAfterCreate": true}
  */
 
@@ -238,6 +238,14 @@ function build_container_spec(string $image, array $body): array
         $spec['privileged'] = true;
     }
 
+    $pod = trim((string) ($body['pod'] ?? ''));
+    if ($pod !== '') {
+        // "pod" joins an existing pod's shared network namespace — verified
+        // live that it can be sent alongside "netns" above without
+        // conflict (podman just defers to the pod's namespace).
+        $spec['pod'] = $pod;
+    }
+
     return $spec;
 }
 
@@ -265,6 +273,17 @@ function containers_list(PodmanClient $client): array
     $out = [];
 
     foreach ($raw as $c) {
+        // Every pod has a hidden "infra" container managing its shared
+        // network namespace — not something a user creates or can
+        // meaningfully stop/remove on its own (found live: it always
+        // shows "running" with no independent lifecycle, so Containers
+        // panel gets a permanently un-removable row once any pod exists;
+        // it already appears as its own row in the Pods panel). See
+        // ajax/pods.php for actual pod lifecycle management.
+        if ($c['IsInfra'] ?? false) {
+            continue;
+        }
+
         $names = $c['Names'] ?? [];
         $name = is_array($names) && count($names) > 0 ? ltrim((string) $names[0], '/') : podman_short_id((string) ($c['Id'] ?? ''));