fix: populate date completed for failed single-repository reports

[rhartuv]

Details

When a report failed via updateWithError / POST /api/v1/reports/failed, the UI showed Finding Failed but Date Completed was blank because report.completedAt only came from input.scan.completed_at, which was never set on failure (SBOM product Date Completed already fell back to error.at).

This change:

1. Sets input.scan.completed_at to the same instant as error.at when marking failed/expired (if not already set).
2. Maps Report.completedAt from scan.completed_at, or from getReportCompletionTime only when an error is present (so in-progress rows do not incorrectly show Date Requested as Date Completed).
3. Unsets completed_at on retry so a retried analysis is not treated as completed.
4. Tightens the completed status filter to require no error field.

(Overview metrics are unchanged: they already exclude documents with an error field.)

Jira

Before:

After:

[vbelouso]

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[zvigrinberg]

@rhartuv LGTM Approved.

[zvigrinberg]

@rhartuv Kindly rebase ,solve conflicts and retest before merging.
Thank you.