Fix Heima account API fallback

[crossagent-production-app]

Refs #26

Summary

• Changed the bundled Heima UI/API fallback from AssetHub Westend to https://explorer-api.heima.network.
• Reused the shared API_HOST constant for the local proxy route so the proxy fallback cannot drift to a different network.
• Added a focused Jest regression test for the default API host.

Diagnosis

The reported Heima sub/account pages were querying the wrong API when NEXT_PUBLIC_API_HOST was empty. Live https://explorer.heima.network/__ENV.js currently exposes NEXT_PUBLIC_API_HOST:""; the UI then fell back to https://assethub-westend-lite.webapi.subscan.io, which returns data:null for both Heima addresses. The Heima backend itself returns account data for both addresses, so this is a frontend/API-host configuration fallback issue, not an address format, indexer, network config, or chain data issue.

Verification

• cd ui-react && npm test -- --runTestsByPath src/__tests__/utils/const.test.ts --runInBand
• cd ui-react && npm run lint -- --file src/utils/const.ts --file src/pages/api/proxy.ts --file src/__tests__/utils/const.test.ts
• cd ui-react && node test-results/evidence/heima-account-e2e.playwright.js
• curl -sS -X POST https://explorer-api.heima.network/api/plugin/balance/account -H 'content-type: application/json' --data '{"address":"49VYuGkjdmZprGpb4jU313RdSffxSVHixojzmafdFYGpVYXb"}'
• curl -sS -X POST https://explorer-api.heima.network/api/plugin/balance/account -H 'content-type: application/json' --data '{"address":"4BNdLBoSrAgW6kHJ5sxVPbGAyqWxqzPF1KbTnWFKf3DVnWj6"}'

Delivery Evidence Summary

Change:
Heima UI fallback API host now resolves to https://explorer-api.heima.network when runtime/build NEXT_PUBLIC_API_HOST is absent, and the Next API proxy shares the same fallback.

Objective Evidence:

• Reproduced current failure mode: live __ENV.js has NEXT_PUBLIC_API_HOST:"", causing the old UI fallback to query assethub-westend-lite.webapi.subscan.io; that endpoint returned data:null for both reported Heima addresses.
• Confirmed Heima backend data exists: explorer-api.heima.network returned balance:"12064779000000000000000000" for 49VYu... and balance:"4477102000000000000000000" for 4BNd....
• Passed focused Jest regression: npm test -- --runTestsByPath src/__tests__/utils/const.test.ts --runInBand.
• Passed focused lint: npm run lint -- --file src/utils/const.ts --file src/pages/api/proxy.ts --file src/__tests__/utils/const.test.ts.
• Passed rendered browser validation: node test-results/evidence/heima-account-e2e.playwright.js; it navigated both account pages, asserted the expected balances rendered, asserted both /api/plugin/balance/account responses used the reported addresses, and asserted zero assethub-westend requests.

Visual Evidence:

Reviewer:
@repo Intake Codex Reviewer

Risks / Not Covered:

• npm run build still fails on existing static prerender errors (NextRouter was not mounted) across many pages; this is outside the narrow API-host fallback change and was not fixed here.
• Production still should set NEXT_PUBLIC_API_HOST explicitly, but this change makes a missing value fall back to the correct Heima API instead of the wrong network.

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Project	Deployment	Actions	Updated (UTC)
subscan-essentials	Ready	Preview, Comment	May 24, 2026 6:25pm
subscan-essentials-ui-react	Ready	Preview, Comment	May 24, 2026 6:25pm