SIWE auth, API proxy fixes, dashboard, login, usage pages

- SIWE auth flow: challenge/login/logout/me API routes + JWT middleware
- Fixed [...path] catch-all: Kubo proxy with matchRoute() + mapToKuboAPI()
- Fixed session_id → nonce field mismatch in AuthProvider
- Fixed dashboard pins crash: Kubo returns {Keys: {...}}, not array
- Added middleware route guard (307 redirect to /login)
- Added login, register, profile, usage, upload pages
- Added dashboard components (StorageGauge, FreeTierProgress)
- Added SWR hooks + AuthGuard + Providers + Toast/ErrorBoundary
- Added payment integration (smart contract ABI, tiers, tokens)
- Fixed IPNS key listing: Name/Id → name/id mapping
- Added PWA support (manifest, service worker, icons)
- Added tests for helpers, limits, search-index, wallet

src/lib/download.ts

@@ -0,0 +1,44 @@
+/* ════════════════════════════ Download ════════════════════════════
+ * Utility om IPFS content te downloaden als bestand.
+ */
+
+/**
+ * Download een bestand van IPFS via de explorer/cat proxy.
+ * Maakt een Blob van de response en simuleert een klik op <a download>.
+ */
+export async function downloadFile(cid: string, filename?: string): Promise<void> {
+  const res = await fetch(`/api/explorer/cat/${encodeURIComponent(cid)}`);
+  if (!res.ok) throw new Error(`Download mislukt (${res.status})`);
+
+  const blob = await res.blob();
+  const url = URL.createObjectURL(blob);
+
+  const ext = filename?.includes('.') ? '' : '.bin';
+  const name = filename || `${cid.slice(0, 12)}${ext}`;
+
+  const a = document.createElement('a');
+  a.href = url;
+  a.download = name;
+  a.rel = 'noopener noreferrer';
+  document.body.appendChild(a);
+  a.click();
+
+  // Cleanup
+  setTimeout(() => {
+    document.body.removeChild(a);
+    URL.revokeObjectURL(url);
+  }, 100);
+}
+
+/**
+ * Download via gateway (alternatief als proxy traag is).
+ */
+export function downloadViaGateway(cid: string, filename?: string) {
+  const gateway = process.env.NEXT_PUBLIC_GATEWAY_URL || 'https://maos.dedyn.io';
+  const a = document.createElement('a');
+  a.href = `${gateway}/ipfs/${cid}`;
+  a.download = filename || cid;
+  a.target = '_blank';
+  a.rel = 'noopener noreferrer';
+  a.click();
+}