fix: show real error text in Account Hub instead of "[object Object]"

[islandbitcoin]

The bug

The Account Hub error dialog shows [object Object] instead of the real reason a mutation failed:

Root cause

Every Flash GraphQL mutation the page calls returns validation failures as an array of { message } objects — e.g. accountUpdateLevel returns errors { message }. All five Account Hub action handlers rendered them with:

message: Array.isArray(result.errors) ? result.errors.join(", ") : result.errors

Array.join calls String() on each element, so [{message: "..."}] becomes "[object Object]". The screenshot is the Change Level action — the mutation returned a real business-logic reason and the UI threw the text away.

The same latent bug was present in all five handlers: Change Level, Lock/Activate, Update Phone, Validate Merchant, Delete Merchant.

The fix

Add a single formatApiErrors() helper that extracts .message from each error object and route all five handlers through it.

• [{message}] (the bug) → renders the actual message
• multiple errors → comma-joined messages
• plain strings / string arrays → unchanged (backward compatible)
• unexpected object shapes → JSON fallback instead of [object Object]

Verification

• node --check passes on the file.
• Exercised the helper against every real error shape; the bug case now renders "Account is already at MERCHANT level" instead of "[object Object]", with no regression on string/array inputs.

Manual test plan (TEST → PROD)

1. Open Admin Panel → Account Hub, select an account.
2. Trigger a mutation that the Flash API will reject — easiest is Change Level to a level the account can't move to (or Lock an already-locked account).
3. Confirm the Error dialog now shows a human-readable reason, not [object Object].

Out of scope (noted, not changed)

The error: callbacks on these same frappe.calls read err?.responseJSON?.exception || err?.message, which doesn't surface the server message when an endpoint returns via the @handle_api_errors decorator (that lands at err.responseJSON.message.error). Genuine 500s currently show the generic "Failed to …" fallback. Happy to follow up separately if wanted.

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