Add version display in admin sidebar footer

- Add /api/version endpoint that returns build info from env vars
- Add version footer to Layout.tsx showing build version, git SHA, and image tag
- Update Dockerfile to accept build args for version info (APP_BUILD_VERSION, APP_GIT_SHA, APP_BUILD_TIME, CONTAINER_IMAGE_TAG)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/src/components/Layout.tsx

@@ -1,6 +1,7 @@
-import { ReactNode } from 'react';
+import { ReactNode, useEffect, useState } from 'react';
 import { useNavigate, useLocation } from 'react-router-dom';
 import { useAuthStore } from '../store/authStore';
+import { api } from '../lib/api';
 import {
   LayoutDashboard,
   Store,
@@ -24,6 +25,13 @@ interface LayoutProps {
   children: ReactNode;
 }
 
+interface VersionInfo {
+  build_version: string;
+  git_sha: string;
+  build_time: string;
+  image_tag: string;
+}
+
 interface NavLinkProps {
   to: string;
   icon: ReactNode;
@@ -69,6 +77,19 @@ export function Layout({ children }: LayoutProps) {
   const navigate = useNavigate();
   const location = useLocation();
   const { user, logout } = useAuthStore();
+  const [versionInfo, setVersionInfo] = useState<VersionInfo | null>(null);
+
+  useEffect(() => {
+    const fetchVersion = async () => {
+      try {
+        const response = await api.get('/version');
+        setVersionInfo(response.data);
+      } catch (error) {
+        console.error('Failed to fetch version info:', error);
+      }
+    };
+    fetchVersion();
+  }, []);
 
   const handleLogout = () => {
     logout();
@@ -206,6 +227,18 @@ export function Layout({ children }: LayoutProps) {
             <span>Logout</span>
           </button>
         </div>
+
+        {/* Version Footer */}
+        {versionInfo && (
+          <div className="px-3 py-2 border-t border-gray-200 bg-gray-50">
+            <p className="text-xs text-gray-500 text-center">
+              {versionInfo.build_version} ({versionInfo.git_sha.slice(0, 7)})
+            </p>
+            <p className="text-xs text-gray-400 text-center mt-0.5">
+              {versionInfo.image_tag}
+            </p>
+          </div>
+        )}
       </div>
 
       {/* Main Content */}