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/api.ts

@@ -123,4 +123,18 @@ export const api = {
       method: "POST",
       body: JSON.stringify({ note }),
     }),
+  listApiKeys: () =>
+    request<{ items: import("./types").ApiKey[] }>("/keys"),
+  createApiKey: (body: {
+    name: string;
+    owner_email?: string;
+    tier?: string;
+    rate_limit_per_min?: number;
+  }) =>
+    request<{ key: string; item: import("./types").ApiKey; warning: string }>(
+      "/keys",
+      { method: "POST", body: JSON.stringify(body) },
+    ),
+  revokeApiKey: (id: string) =>
+    request<{ status: string }>(`/keys/${id}`, { method: "DELETE" }),
 };