Add container pause/resume/kill/rename + reusable context-menu component

First increment of the big WebUI feature-parity spec (see task list) —
row-level actions were about to run out of icon-button space, so this adds
a small anchored dropdown menu (app.js openContextMenu) for secondary
per-container actions instead of cramming more buttons into every row.

All four new actions verified live against the real podman API before
wiring up the UI (same discipline as the CSRF/pull/compose bugs found
earlier — field names and response shapes checked against the running
socket, not assumed from docs).

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

webui/plugins/podman/include/PodmanClient.php

@@ -138,6 +138,27 @@ final class PodmanClient
         $this->request('DELETE', '/containers/' . rawurlencode($id), ['force' => $force ? 'true' : 'false'], true);
     }
 
+    public function pauseContainer(string $id): void
+    {
+        $this->request('POST', '/containers/' . rawurlencode($id) . '/pause', [], true);
+    }
+
+    public function unpauseContainer(string $id): void
+    {
+        $this->request('POST', '/containers/' . rawurlencode($id) . '/unpause', [], true);
+    }
+
+    /** $signal accepts both a name ("SIGKILL") and a bare number, matching libpod's own `kill?signal=` parsing. */
+    public function killContainer(string $id, string $signal = 'SIGKILL'): void
+    {
+        $this->request('POST', '/containers/' . rawurlencode($id) . '/kill', ['signal' => $signal], true);
+    }
+
+    public function renameContainer(string $id, string $newName): void
+    {
+        $this->request('POST', '/containers/' . rawurlencode($id) . '/rename', ['name' => $newName], true);
+    }
+
     /**
      * GET /containers/{id}/logs — returns the raw (already de-multiplexed
      * where possible) log text. Podman's non-TTY log stream uses the same