fix: harden wallet request errors

[Sikkra]

Summary

• re-enable request cleanup callbacks after fetch/network failures so the Send form is not left disabled
• escape untrusted RPC/explorer error text before rendering it in SweetAlert HTML
• keep existing CORS help link markup intact while sanitizing the underlying error message

Verification

• .\node_modules\.bin\eslint.cmd --rule "linebreak-style: 0" src\api.js src\utils.js src\send\send.js
• node -e "for (const file of ['src/utils.js','src/api.js','src/send/send.js']) { new Function(require('fs').readFileSync(file,'utf8')); console.log(file + ' parses'); }"
• git diff --check

Note: npm test is currently blocked on Windows by the pre-existing quoted glob script (eslint 'src/*.js'), which is addressed separately in PR #3.

Bounty payout address if approved: USDT TRC20 TPwPFww7zxXFQ7zugo22gktQhckWVarRqi