feat(search+docs): trigram fuzzy search, brand/country filters, developer docs

Search:
- migration 0009: trigram GIN index on brand.name + btree on country_of_origin
- SearchProducts: typo-tolerant word_similarity matching (>=0.42) on top of
  ILIKE substring + barcode; new brand/country filters; rank by
  similarity * (0.5 + quality_score). Response gains country_of_origin,
  quality_score and per-result relevance score.
- public search UI: brand/country filter inputs; show country in results

Docs:
- serve embedded OpenAPI 3 spec at GET /api/v1/openapi.json (not rate limited)
- ApiDocs page: auth + rate-limit section, updated search params/response
- docs/api.md developer guide

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

public-frontend/src/components/Home.tsx

@@ -13,6 +13,8 @@ export default function Home({
   onApi: () => void;
 }) {
   const [q, setQ] = useState("");
+  const [brand, setBrand] = useState("");
+  const [country, setCountry] = useState("");
   const [items, setItems] = useState<ProductSummary[]>([]);
   const [total, setTotal] = useState(0);
   const [searched, setSearched] = useState(false);
@@ -24,7 +26,10 @@ export default function Home({
     setLoading(true);
     setError("");
     try {
-      const res = await api.search(q.trim(), 1, 30);
+      const res = await api.search(q.trim(), 1, 30, {
+        brand: brand.trim() || undefined,
+        country: country.trim() || undefined,
+      });
       setItems(res.items);
       setTotal(res.total);
       setSearched(true);
@@ -61,6 +66,20 @@ export default function Home({
             {loading ? "检索中…" : "检索"}
           </button>
         </form>
+        <div className="mt-3 max-w-2xl mx-auto flex flex-wrap items-center justify-center gap-2 text-sm">
+          <input
+            value={brand}
+            onChange={(e) => setBrand(e.target.value)}
+            placeholder="按品牌筛选（如 Ferrero）"
+            className="flex-1 min-w-[14rem] bg-white border rounded-lg px-3 py-2 outline-none focus:ring-2 focus:ring-emerald-300"
+          />
+          <input
+            value={country}
+            onChange={(e) => setCountry(e.target.value)}
+            placeholder="按产地筛选（如 China）"
+            className="flex-1 min-w-[14rem] bg-white border rounded-lg px-3 py-2 outline-none focus:ring-2 focus:ring-emerald-300"
+          />
+        </div>
         <button
           onClick={onApi}
           className="mt-4 inline-flex items-center gap-1.5 text-sm text-emerald-700 hover:underline"
@@ -105,7 +124,12 @@ export default function Home({
                         {p.gtin ? ` · ${p.gtin}` : ""}
                       </div>
                     </div>
-                    <span className="text-xs text-gray-400">{p.category_path || ""}</span>
+                    <span className="text-xs text-gray-400 text-right">
+                      <span className="block">{p.category_path || ""}</span>
+                      {p.country_of_origin ? (
+                        <span className="block text-gray-400">产地：{p.country_of_origin}</span>
+                      ) : null}
+                    </span>
                   </button>
                 </li>
               ))}