Gas floor fix, chain guard, and dashboard footer

- wallet.js: fetch correct EIP-1559 fees from the network (Amoy/Polygon Bor
  enforce a ~25-30 gwei priority floor MetaMask's estimate misses) via new
  /api/gas; hard chain-guard before signing so a tx never lands on the wrong
  network; accept the wallet's usual networks in AppKit so its modal stops
  looping and drive add+switch ourselves.
- chain.js: suggestedFees() from eth_maxPriorityFeePerGas + base fee.
- Dashboard: move the Site links (Ad packages / Live ledger / The contract)
  out of the sidebar into a page footer; hide the sidebar scrollbar.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server.js

@@ -503,6 +503,11 @@ const server = http.createServer(async (req, res) => {
       await auth.logout(req);
       return json(res, 200, { ok: true }, { 'Set-Cookie': auth.clearCookie() });
     }
+    if (p === '/api/gas' && req.method === 'GET') {
+      try { return json(res, 200, await chain.suggestedFees()); }
+      catch (e) { return json(res, 200, {}); }
+    }
+
     if (p === '/api/me' && req.method === 'GET') {
       const s = await auth.fromRequest(req);
       if (!s) return json(res, 200, { signedIn: false });