Add Create Container UI and Templates (Unraid XML) feature

Lets users create containers from the WebUI (image/name/ports/volumes/
env/network mode/restart policy/privileged) instead of only managing
existing ones, and adds a Templates panel to save/reuse those configs
as Unraid-Docker-compatible template XML, including browsing and
importing the host's own existing Docker Manager templates directly.

Also fixes bugs found via live testing along the way: container names
with spaces/invalid characters now get a clear client- and server-side
error with a suggested fix instead of podman's raw API error, the New
Container modal's backdrop no longer renders transparent (was being
appended outside the .podman-plugin CSS scope), and modal buttons now
have real visual hierarchy (ghost/primary/danger) after Unraid's own
site-wide button theme was found to override plain single-class rules.

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

webui/plugins/podman/Podman.page

@@ -54,6 +54,7 @@ function podman_asset_version(string $relPath): string
   <nav class="podman-subnav">
     <button class="active" data-panel="dashboard">Dashboard</button>
     <button data-panel="containers">Containers</button>
+    <button data-panel="templates">Templates</button>
     <button data-panel="pods">Pods</button>
     <button data-panel="images">Images</button>
     <button data-panel="volumes">Volumes</button>
@@ -99,6 +100,9 @@ function podman_asset_version(string $relPath): string
       </div>
     </section>
 
+    <!-- ============================= TEMPLATES ============================= -->
+    <section class="podman-panel" id="podman-panel-templates"></section>
+
     <!-- ============================= PODS ============================= -->
     <section class="podman-panel" id="podman-panel-pods"></section>
 
@@ -261,7 +265,7 @@ function podman_asset_version(string $relPath): string
 
 <?php
 foreach ([
-    'app', 'dashboard', 'containers', 'pods', 'images', 'volumes',
+    'app', 'dashboard', 'containers', 'templates', 'pods', 'images', 'volumes',
     'networks', 'logs', 'terminal', 'compose', 'settings',
 ] as $podmanJsModule) {
     $podmanJsPath = "/javascript/{$podmanJsModule}.js";