Fix SIWE chain-mismatch: switch wallet to Polygon 137 before sign-in and members-area unlock

public/my.js

@@ -319,6 +319,9 @@
       const eth=await window.RMCWallet.pick();
       if(!eth){err.textContent='No wallet found in this browser. On a phone, open your wallet app (SafePal, Phantom, MetaMask, Trust, Coinbase…), go to its Browser or DApp tab, and type this page\'s address there — your wallet connects automatically.';return;}
       const accs=await eth.request({method:'eth_requestAccounts'});const account=accs[0];
+      // Match the wallet's active chain to the SIWE message's Chain ID (137),
+      // or the wallet rejects the signature ("chain ID does not match").
+      try{await window.RMCWallet.ensureChain(eth);}catch(ce){err.textContent='Please switch your wallet to the Polygon network, then tap Connect again. (Your wallet blocks sign-in when it\'s on a different network.)';return;}
       const ch=await(await fetch('/api/public/msg-challenge',{method:'POST',headers:{'Content-Type':'application/json'},body:JSON.stringify({address:account})})).json();
       if(!ch.message)throw new Error(ch.error||'Could not start sign-in.');
       let hex='0x';for(const b of new TextEncoder().encode(ch.message))hex+=b.toString(16).padStart(2,'0');