fix: normalize BGL bridge submit endpoint

[tolga-tom-nook]

Summary

Normalizes the BGL bridge submit endpoint before appending /submit/bgl.

The default bridge endpoint includes a trailing slash:

this.bridgeEndpoint = config.bridgeEndpoint || 'https://bglswap.com/app/'

But _submitToBridge appended another slash:

`${this.bridgeEndpoint}/submit/bgl`

That produces https://bglswap.com/app//submit/bgl for the default/configured endpoint. This PR trims trailing slashes first so both https://bglswap.com/app/ and https://bglswap.com/app resolve to the canonical https://bglswap.com/app/submit/bgl URL.

Validation

Focused regression test:

npx jest src/__tests__/BGLBridgeEndpoint.test.ts --runInBand --coverage=false

Result:

PASS src/__tests__/BGLBridgeEndpoint.test.ts
Test Suites: 1 passed, 1 total
Tests: 2 passed, 2 total

Targeted lint:

npx eslint src/bridge/BGL.ts src/__tests__/BGLBridgeEndpoint.test.ts --ext .ts

Result: passed.

Diff hygiene:

git diff --check

Result: clean.

Note: npm run build is currently blocked by the repo's dependency/toolchain mismatch after fresh install (@types/node requires disposable lib symbols not available to the pinned TypeScript 4.9 toolchain). The focused Jest regression and targeted ESLint pass for this change.

Bounty context: Bitgesell PR bounty/improvement program.

[MyTH-zyxeon]

Review assist for maintainers:

This looks like a focused bridge endpoint-normalization fix: _submitToBridge now trims trailing slashes from bridgeEndpoint before appending /submit/bgl, and the new Jest coverage exercises both trailing-slash and no-trailing-slash configurations against a mocked _post. I checked the patch scope and did not see wallet/key generation, transaction signing, provider/RPC, or live bridge submission behavior changes beyond URL construction.

Suggested merge checks:

• Run the new BGLBridgeEndpoint Jest test and confirm it does not require real EVM/BGL keys, RPC access, or a live bridge endpoint because _post is mocked.
• Add or manually verify edge cases for multiple trailing slashes if the SDK accepts arbitrary user-provided endpoint strings, since the implementation uses replace(/\/+$/, "").
• Confirm the normalized URL preserves non-root path prefixes such as https://bglswap.com/app and does not change header/body payload construction.

Main acceptance criterion: bridge submissions should deterministically call exactly one /submit/bgl path segment for both bridgeEndpoint forms, without changing signing/key/runtime behavior.