Store report closure reason and impact field

[tikket1]

Context

Two related gaps in report metadata:

1. No closure reason/code

When a report is closed, H1 provides a reason (duplicate, informative, not-applicable, spam, etc.) but we only store state and substate. The substate partially covers this but the explicit closure code is more reliable.

2. No impact field

H1 reports have a separate impact field distinct from vulnerability_information. This is the researcher's stated impact assessment, often structured differently from the technical details.

Missing Fields

• closed_reason or resolution — why the report was closed
• impact — impact description text (separate from vuln info)

Changes Needed

1. Add closed_reason: str | None and impact: str | None columns to Report model
2. Extract attrs.get("closed_reason") and attrs.get("impact") in adapter
3. Add to ReportData, schemas, and API response
4. Show impact in report detail view alongside vulnerability_information