Fix config flow: button text and error message

[marcinbauer-ohf]

Proposed change

Two bug fixes in the config flow dialog:

1. "Skip and finish" button text when area picker is cleared

Clearing the area picker still added the device to _deviceUpdate with an empty area value, making Object.keys(_deviceUpdate).length truthy. This caused the button to show "Finish" instead of "Skip and finish" even when no area was selected.

Fix checks for meaningful updates (non-empty name or area) using .some() instead of just checking for entry presence.

2. Config flow error showing "Unknown error" instead of actual message

handleFetchPromise throws a plain object { error, body, status_code }, not a standard Error instance, so err.message is always undefined. The error handler only checked err.message || err.body, missing err.error entirely. Every network-level failure (connection refused, CORS, etc.) showed "Unknown error".

Fix checks in priority order: err.message → err.body.message (when body is a JSON object) → err.body → err.error → "Unknown error".

Screenshots

No visual changes (button text fix is behavioral, error message fix only affects error dialogs).

Type of change

• Bugfix (non-breaking change which fixes an issue)

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue or discussion:
• Link to documentation pull request:
• Link to developer documentation pull request:
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Checklist

• I understand the code I am submitting and can explain how it works.
• The code change is tested and works locally.
• There is no commented out code in this PR.
• I have followed the perfect PR recommendations
• Any generated code has been carefully reviewed for correctness and compliance with project standards.

To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.