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/javascript/volumes.js

@@ -24,8 +24,8 @@
       '<td><span class="podman-chip podman-chip-neutral">' + P.escapeHtml(v.driver) + '</span></td>' +
       '<td class="mono podman-row-sub">' + pathCell + '</td>' +
       '<td class="tnum">' + v.usedBy + '</td>' +
-      '<td class="podman-actions"><button class="podman-btn podman-btn-icon" data-action="remove"' +
-      (v.usedBy > 0 ? ' disabled title="In use by a container"' : ' title="Remove"') + '>&#128465;</button></td>' +
+      '<td class="podman-actions"><div class="podman-actions-row"><button class="podman-btn podman-btn-icon" data-action="remove"' +
+      (v.usedBy > 0 ? ' disabled title="In use by a container"' : ' title="Remove"') + '>&#128465;</button></div></td>' +
       '</tr>';
   }