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>

public/index.html

@@ -439,7 +439,7 @@
 </section>
 
 <script src="/assets/common.js?v=20260908c"></script>
-<script src="/assets/wallet.js?v=20260908m"></script>
+<script src="/assets/wallet.js?v=20260908n"></script>
 <script src="/assets/home.js?v=20260906m"></script>
 <script src="/assets/chat.js?v=20260906m"></script>
 </body>