fix: show BGL deposit submit errors

[Sikkra]

Summary

When /submit/bgl returns an error response, the frontend currently only logs to the console and leaves the user on the same form with no visible feedback. This makes the Continue button appear to flash and then do nothing.

This PR displays the bridge service error message in-page and falls back to a generic BGL deposit-address error for malformed responses or rejected requests.

Verification

• CI=true npm test -- --watchAll=false in app/ (1 passed)
• git diff --check
• node --openssl-legacy-provider ./node_modules/react-scripts/scripts/build.js in app/ (compiled with existing warnings)

Related: #28
Program reference: BitgesellOfficial/bitgesell#81

USDT-TRC20 payout address if accepted: TPwPFww7zxXFQ7zugo22gktQhckWVarRqi

[MyTH-zyxeon]

Maintainer-facing review assist for the #81 bounty queue:

This is a useful UX fix: /submit/bgl failures currently look like a no-op to the user, and this PR makes the bridge service error visible in-page while adding a regression test for the rejected response path.

Acceptance checks I would use before merge:

• Please normalize the touched BglToWbgl file back to the repository's existing line endings before merge. The functional change is small, but the current diff appears to rewrite most of the component with CRLF, which makes review and future cherry-picks noisier than necessary.
• Keep the new setError(null) before submission so a stale previous error cannot remain after a successful retry.
• Confirm both service-reported errors and malformed/rejected responses show a user-visible fallback via role="alert".
• Run the stated checks from a clean app/ install: CI=true npm test -- --watchAll=false, git diff --check, and the existing React build command.
• For bounty accounting, tie this explicitly back to BGL (Bitgesell) Bounty/Improvement Program ($50000 budget) bitgesell#81 after approval so maintainers and submitter agree which program is reviewing it.

No payment action or claim from me here; just a focused review pass to help maintainers evaluate the PR.