feat: show server version in sidebar header

Version injected at build time via VITE_APP_VERSION env var.
CI sets it to branch@sha. Falls back to 'dev' in local dev.
Displayed next to "Cameleer" in the sidebar header.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/components/LayoutShell.tsx

@@ -500,6 +500,7 @@ function LayoutContent() {
       <Sidebar.Header
         logo={camelLogo}
         title="Cameleer"
+        version={__APP_VERSION__}
       />
 
       {/* Applications section */}