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

public/icon-192.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="192" height="192" viewBox="0 0 192 192">
+  <rect width="192" height="192" rx="32" fill="#0891b2"/>
+  <text x="96" y="108" font-family="system-ui, sans-serif" font-size="96" font-weight="bold" fill="white" text-anchor="middle">M</text>
+</svg>