fix(report): deduplicate consecutive headings in scan report

[vardhans07]

Closes #1332

Description

Resolves an issue where Markdown reports contain consecutive duplicate section headings (e.g., # Executive Summary).

Changes

• Added deduplicate_markdown_headings helper in strix/report/writer.py.
• Applied deduplication to final_scan_result before file writing in write_execution_report.
• Added unit tests in tests/test_report_writer.py.

[greptile-apps]

Confidence Score: 2/5

This PR is not safe to merge because the report module cannot load through its existing production import, and the renamed writer also fails whenever invoked.

Findings

1.  Report writer rename breaks imports ▶
2.  Undefined timezone breaks reports ▶
3.  Deduplication corrupts fenced content ▶

Fix with agent prompt

### Issue 1
strix/report/writer.py:160
Renaming `write_executive_report` without updating its production import and caller makes `strix.report.state` fail to import because the old symbol no longer exists. This prevents report state initialization and scan artifact generation. The existing writer test also still calls the removed name.

### Issue 2
strix/report/writer.py:165
`write_execution_report` references `timezone.utc`, but this module imports only `UTC` and `datetime`. Every call therefore raises `NameError` after opening the output file and writing its title, leaving a partial report instead of the completed artifact.

```suggestion
        f.write(f"**Generated:** {datetime.now(UTC).strftime('%Y-%m-%d %H:%M:%S UTC')}\n\n")
```

### Issue 3
strix/report/writer.py:147-151
The deduplicator treats heading-shaped lines inside fenced code blocks as document headings. Final report fields may contain fenced payload excerpts, so two identical `#`-prefixed lines in an excerpt will lose one line and corrupt the report evidence. The helper needs to preserve fenced content verbatim.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

Summary

This PR adds normalization of consecutive Markdown headings before writing the penetration-test report and adds focused unit coverage.

• Introduces deduplicate_markdown_headings.
• Renames the report writer and applies normalization to its input.
• Adds direct helper and report-output tests.
• The current rename and datetime reference break report generation, while block-agnostic normalization can alter fenced payload excerpts.

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