ci: tolerate missing preview URL output

[yomna-shousha]

Summary

• tolerate Wrangler preview output that omits preview/deployment URL arrays
• derive fallback preview and deployment URLs from preview_slug/deployment_id while keeping custom preview names working

Verification

• reproduced the existing jq failure with successful preview output missing URL arrays: exit=4
• verified the updated jq filter against failed-log output shape
• verified it still handles previous output with preview_urls/deployment_urls
• verified custom preview_slug fallback output
• ran git diff --check

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Latest commit: 082e055

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commit: 082e055

[yomna-shousha]

Closing this because deriving preview URLs in the workflow would mask the real problem: Wrangler is not returning preview/deployment URLs, and the expected preview hostnames do not resolve.