chore: metamask networks, explorer SPA, nginx scripts; ignore Python cache

- Dual-chain / GRU deployment JSON sync
- Frontend explorer SPA + MetaMask components
- Scripts: nginx fixes, link deploy, local SPA serve helper
- Token icon chain-138.png; .gitignore __pycache__

Co-authored-by: Cursor <cursoragent@cursor.com>

scripts/serve_explorer_spa.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python3
+"""Static explorer with SPA fallback: unknown paths serve index.html (client router).
+API paths (/api/, /explorer-api/) are not rewritten so missing backends still 404 clearly."""
+from __future__ import annotations
+
+import argparse
+import os
+import sys
+from http.server import SimpleHTTPRequestHandler, ThreadingHTTPServer
+from urllib.parse import urlparse
+
+
+def main() -> int:
+    p = argparse.ArgumentParser(description="Serve explorer-monorepo/frontend/public with SPA fallback.")
+    p.add_argument("port", nargs="?", type=int, default=8080, help="Listen port (default 8080)")
+    p.add_argument(
+        "--bind",
+        default="127.0.0.1",
+        help="Bind address (default 127.0.0.1)",
+    )
+    args = p.parse_args()
+    script_dir = os.path.dirname(os.path.abspath(__file__))
+    root = os.path.normpath(os.path.join(script_dir, "..", "frontend", "public"))
+    if not os.path.isfile(os.path.join(root, "index.html")):
+        print(f"ERROR: index.html not found under {root}", file=sys.stderr)
+        return 1
+
+    class Handler(SimpleHTTPRequestHandler):
+        def __init__(self, *a, **kw):
+            super().__init__(*a, directory=root, **kw)
+
+        def do_GET(self) -> None:  # noqa: N802
+            path = urlparse(self.path).path
+            if path.startswith("/api/") or path.startswith("/explorer-api"):
+                return super().do_GET()
+            rel = path.lstrip("/")
+            if rel.startswith(".."):
+                self.send_error(403, "Forbidden")
+                return
+            fs = os.path.join(root, rel) if rel else root
+            if os.path.isfile(fs):
+                return super().do_GET()
+            self.path = "/index.html"
+            return super().do_GET()
+
+    httpd = ThreadingHTTPServer((args.bind, args.port), Handler)
+    print(f"Serving SPA explorer: http://{args.bind}:{args.port}/  (root={root})", flush=True)
+    try:
+        httpd.serve_forever()
+    except KeyboardInterrupt:
+        print("\nStopped.", flush=True)
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())