Add Strix scan parser

[ummon-v]

Description

Adds a new parser for Strix, importing the vulnerabilities.json report of a Strix security run under the "Strix Scan" scan type.

• One Finding per report entry; every field is optional per finding_class (code findings carry PoC/CVSS data, dependency findings carry package metadata), missing fields are left unset
• Maps title, severity, impact, description (target/confidence/CVSS lines plus the analysis sections), steps to reproduce (PoC), mitigation (remediation steps + fix effort), CWE, CVE, CVSS score and vector, date, file_path/line from code locations, component name/version for dependency findings, and static/dynamic from finding_class
• Unknown or missing severities default to Info
• A non-array report raises an error instead of importing 0 findings; a wrapped {"vulnerabilities": [...]} shape is accepted for forward compatibility
• Deduplication uses unique_id_from_tool, keyed on the report's stable per-finding id (registered in settings.dist.py)

Test results

• unittests.tools.test_strix_parser: 15 tests covering no/one/many findings, full field mapping, dependency and code-location mapping, severity defaults, CWE extraction, CVSS vector assembly, wrapped report shape, and malformed input rejection
• unittests.test_parsers meta-test passes (layout and docs checks)
• Ruff clean (0.16.5)

Documentation

• New parser page: docs/content/supported_tools/parsers/file/strix.md

Checklist

• Rebased against the very latest dev
• Submitted against dev (new feature)
• Ruff compliant
• Python 3.13 compliant
• Documentation added under docs/
• No model changes (no migrations needed)
• Unit tests added
• Labels applied