fix: add frontend/src/lib/ to git (was ignored by /lib/ pattern)

The root .gitignore had `lib/` which matched frontend/src/lib/,
causing Docker build to fail with "Module not found: Can't resolve
'@/lib/utils'" and '@/lib/i18n'.

Changed to `/lib/` so it only ignores the Python lib at repo root.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/lib/webllm.ts

@@ -0,0 +1,46 @@
+import { useState, useCallback } from "react";
+
+interface WebLLMState {
+  isLoaded: boolean;
+  loading: boolean;
+  error: string | null;
+}
+
+export function useWebLLM() {
+  const [state, setState] = useState<WebLLMState>({
+    isLoaded: false,
+    loading: false,
+    error: null,
+  });
+
+  const isWebGPUSupported = useCallback(() => {
+    if (typeof navigator === "undefined") return false;
+    return "gpu" in navigator;
+  }, []);
+
+  const translate = useCallback(
+    async (
+      _text: string,
+      _targetLang: string,
+      _systemPrompt?: string,
+      _glossary?: string,
+    ): Promise<string> => {
+      setState((s) => ({ ...s, loading: true, error: null }));
+      try {
+        throw new Error("WebLLM is not available in this environment");
+      } catch (err) {
+        const message =
+          err instanceof Error ? err.message : "WebLLM translation failed";
+        setState((s) => ({ ...s, loading: false, error: message }));
+        throw err;
+      }
+    },
+    [],
+  );
+
+  return {
+    ...state,
+    isWebGPUSupported,
+    translate,
+  };
+}