feat(api): API keys + Redis rate limiting + usage stats

Add an optional API-key layer to the public read-only API. Keys grant
higher per-minute rate limits and attribute usage; anonymous callers are
still allowed at a lower IP-based budget.

- migration 0008_api_key: api_key table (sha256 hash only, plaintext shown once)
- apikey pkg: key generation + hashing
- ratelimit pkg: Redis fixed-window limiter + per-key usage counters; fails open
- public API middleware: X-API-Key / Bearer auth, X-RateLimit-* headers, 429+Retry-After
- admin: issue/list/revoke keys + usage view (API + UI tab)

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

admin-frontend/src/App.tsx

@@ -4,9 +4,10 @@ import Login from "./components/Login";
 import ProductList from "./components/ProductList";
 import ProductDetail from "./components/ProductDetail";
 import SubmissionsPage from "./components/SubmissionsPage";
-import { Inbox, LogOut, Package } from "lucide-react";
+import ApiKeysPage from "./components/ApiKeysPage";
+import { Inbox, KeyRound, LogOut, Package } from "lucide-react";
 
-type Tab = "products" | "submissions";
+type Tab = "products" | "submissions" | "keys";
 type View = { name: "list" } | { name: "detail"; id: string };
 
 export default function App() {
@@ -99,6 +100,16 @@ export default function App() {
                 </span>
               )}
             </button>
+            <button
+              onClick={() => setTab("keys")}
+              className={`px-3 py-1.5 rounded-md flex items-center gap-1.5 ${
+                tab === "keys"
+                  ? "bg-emerald-50 text-emerald-700"
+                  : "text-gray-600 hover:bg-gray-100"
+              }`}
+            >
+              <KeyRound className="h-4 w-4" /> API 密钥
+            </button>
           </nav>
         </div>
         <div className="flex items-center gap-4 text-sm text-gray-600">
@@ -112,7 +123,9 @@ export default function App() {
         </div>
       </header>
       <main className="flex-1 overflow-auto p-6">
-        {tab === "submissions" ? (
+        {tab === "keys" ? (
+          <ApiKeysPage />
+        ) : tab === "submissions" ? (
           <SubmissionsPage onPending={setPending} />
         ) : view.name === "list" ? (
           <ProductList onOpen={(id) => setView({ name: "detail", id })} />