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/app.js

@@ -252,15 +252,25 @@ window.Podman = (function () {
         (item.disabled ? ' disabled' : '') + '>' + escapeHtml(item.label) + '</button>';
     }).join('');
 
+    // Viewport-relative (see the "position: fixed" comment on
+    // .podman-context-menu in podman.css) — no scrollY/scrollX added.
     const rect = anchorEl.getBoundingClientRect();
-    menu.style.top = (rect.bottom + window.scrollY + 4) + 'px';
-    menu.style.left = (rect.right + window.scrollX - 180) + 'px';
+    menu.style.top = (rect.bottom + 4) + 'px';
+    menu.style.left = (rect.right - 180) + 'px';
     (document.querySelector('.podman-plugin') || document.body).appendChild(menu);
 
+    // menu.children includes the separator <div>s too, so indexing into it
+    // directly (by a counter that only advances for real items) drifts by
+    // one after every separator — e.g. "Remove" (after a separator) ended
+    // up wired to the separator <div> instead of its own <button>, so
+    // clicking it did nothing. querySelectorAll('button') only ever
+    // returns the actual buttons, in the same order as the non-separator
+    // items, so indexing into that stays aligned regardless of separators.
+    const buttons = menu.querySelectorAll('button');
     let buttonIndex = 0;
     items.forEach(function (item) {
       if (item === 'separator') return;
-      const btn = menu.children[buttonIndex];
+      const btn = buttons[buttonIndex];
       buttonIndex++;
       if (item.disabled) return;
       btn.addEventListener('click', function (e) {