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/types.ts

@@ -137,6 +137,25 @@ export interface SubmissionDetail {
   existing_product?: ProductDetail;
 }
 
+export interface ApiKeyUsage {
+  total: number;
+  today: number;
+  last_used_at?: number | null;
+}
+
+export interface ApiKey {
+  id: string;
+  name: string;
+  key_prefix: string;
+  owner_email: string | null;
+  tier: string;
+  rate_limit_per_min: number;
+  revoked_at: string | null;
+  created_by: string | null;
+  created_at: string;
+  usage: ApiKeyUsage;
+}
+
 export const FIELD_LABELS: Record<string, string> = {
   name: "名称",
   gtin: "条码",