Rename AuthMode to Backend, fix LiteLLM variant typo, add image update alerts, clean up Settings

- Fix serde deserialization error: TypeScript sent "lit_llm" but Rust expected "lite_llm"
- Rename AuthMode enum to Backend across Rust and TypeScript (with serde alias for backward compat)
- Add container image update checking via registry digest comparison
- Improve Settings page: fix image address display spacing, remove per-project auth section
- Update UI labels from "Auth" to "Backend" throughout

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/src/components/settings/ImageUpdateDialog.tsx

@@ -0,0 +1,91 @@
+import { useEffect, useRef, useCallback } from "react";
+import type { ImageUpdateInfo } from "../../lib/types";
+
+interface Props {
+  imageUpdateInfo: ImageUpdateInfo;
+  onDismiss: () => void;
+  onClose: () => void;
+}
+
+export default function ImageUpdateDialog({
+  imageUpdateInfo,
+  onDismiss,
+  onClose,
+}: Props) {
+  const overlayRef = useRef<HTMLDivElement>(null);
+
+  useEffect(() => {
+    const handleKeyDown = (e: KeyboardEvent) => {
+      if (e.key === "Escape") onClose();
+    };
+    document.addEventListener("keydown", handleKeyDown);
+    return () => document.removeEventListener("keydown", handleKeyDown);
+  }, [onClose]);
+
+  const handleOverlayClick = useCallback(
+    (e: React.MouseEvent<HTMLDivElement>) => {
+      if (e.target === overlayRef.current) onClose();
+    },
+    [onClose],
+  );
+
+  const shortDigest = (digest: string) => {
+    // Show first 16 chars of the hash part (after "sha256:")
+    const hash = digest.startsWith("sha256:") ? digest.slice(7) : digest;
+    return hash.slice(0, 16);
+  };
+
+  return (
+    <div
+      ref={overlayRef}
+      onClick={handleOverlayClick}
+      className="fixed inset-0 bg-black/50 flex items-center justify-center z-50"
+    >
+      <div className="bg-[var(--bg-secondary)] border border-[var(--border-color)] rounded-lg p-6 w-[28rem] max-h-[80vh] overflow-y-auto shadow-xl">
+        <h2 className="text-lg font-semibold mb-3">Container Image Update</h2>
+
+        <p className="text-sm text-[var(--text-secondary)] mb-4">
+          A newer version of the container image is available in the registry.
+          Re-pull the image in Docker settings to get the latest tools and fixes.
+        </p>
+
+        <div className="space-y-2 mb-4 text-xs bg-[var(--bg-primary)] rounded p-3 border border-[var(--border-color)]">
+          {imageUpdateInfo.local_digest && (
+            <div className="flex justify-between">
+              <span className="text-[var(--text-secondary)]">Local digest</span>
+              <span className="font-mono text-[var(--text-primary)]">
+                {shortDigest(imageUpdateInfo.local_digest)}...
+              </span>
+            </div>
+          )}
+          <div className="flex justify-between">
+            <span className="text-[var(--text-secondary)]">Remote digest</span>
+            <span className="font-mono text-[var(--accent)]">
+              {shortDigest(imageUpdateInfo.remote_digest)}...
+            </span>
+          </div>
+        </div>
+
+        <p className="text-xs text-[var(--text-secondary)] mb-4">
+          Go to Settings &gt; Docker and click &quot;Re-pull Image&quot; to update.
+          Running containers will not be affected until restarted.
+        </p>
+
+        <div className="flex items-center justify-end gap-2">
+          <button
+            onClick={onDismiss}
+            className="px-3 py-1.5 text-xs text-[var(--text-secondary)] hover:text-[var(--text-primary)] transition-colors"
+          >
+            Dismiss
+          </button>
+          <button
+            onClick={onClose}
+            className="px-3 py-1.5 text-xs bg-[var(--bg-tertiary)] border border-[var(--border-color)] rounded hover:bg-[var(--border-color)] transition-colors"
+          >
+            Close
+          </button>
+        </div>
+      </div>
+    </div>
+  );
+}