WalletConnect buy: stop overriding gas (let wallet set fees)

Setting fees made MetaMask show an unclearable "site-suggested fee" alert. Hand
fee control back to the wallet; its own estimate meets Amoy's minimum.

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

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@@ -696,7 +696,7 @@
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 <script src="/assets/common.js?v=20260908c"></script>
-<script src="/assets/wallet.js?v=20260908i"></script>
+<script src="/assets/wallet.js?v=20260908j"></script>
 <script src="/assets/my.js?v=20260908k"></script>
 <script src="/assets/chat.js?v=20260907l"></script>
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