Expand ecash explorer capabilities

Add Fedimint discovery, dual SQLite/Postgres storage, richer review handling, and generated social imagery.

api/src/http.ts

@@ -0,0 +1,39 @@
+/**
+ * Read a response body up to `maxBytes`, or refuse it.
+ *
+ * `res.arrayBuffer()` and `res.json()` buffer however much the server sends before any
+ * size check can run, and a mint is an untrusted server: the abort timer bounds how
+ * *long* a read may take, this bounds how *large* it may get, and both are needed. The
+ * Content-Length header is checked first as a courtesy — a chunked or lying response
+ * still hits the streaming cap.
+ *
+ * Returns null when the body is over the limit or unreadable. The caller treats that
+ * exactly like a failed fetch.
+ */
+export async function readBodyBounded(res: Response, maxBytes: number): Promise<Buffer | null> {
+  const declared = Number(res.headers.get('content-length') ?? '');
+  if (Number.isFinite(declared) && declared > maxBytes) return null;
+
+  const reader = res.body?.getReader();
+  if (!reader) return null;
+
+  const chunks: Uint8Array[] = [];
+  let size = 0;
+  try {
+    for (;;) {
+      const { done, value } = await reader.read();
+      if (done) break;
+      size += value.byteLength;
+      if (size > maxBytes) {
+        await reader.cancel().catch(() => undefined);
+        return null;
+      }
+      chunks.push(value);
+    }
+  } catch {
+    // Aborted by the caller's timer, or the connection died mid-body.
+    return null;
+  }
+
+  return Buffer.concat(chunks);
+}