feat(reporting): add LLM-based vulnerability deduplication

- Add dedupe.py with XML-based LLM deduplication using direct litellm calls
- Integrate deduplication check in create_vulnerability_report tool
- Add get_existing_vulnerabilities() method to tracer for fetching reports
- Update schema and system prompt with deduplication guidelines

strix/agents/StrixAgent/system_prompt.jinja

@@ -134,6 +134,7 @@ VALIDATION REQUIREMENTS:
 - Keep going until you find something that matters
 - A vulnerability is ONLY considered reported when a reporting agent uses create_vulnerability_report with full details. Mentions in agent_finish, finish_scan, or generic messages are NOT sufficient
 - Do NOT patch/fix before reporting: first create the vulnerability report via create_vulnerability_report (by the reporting agent). Only after reporting is completed should fixing/patching proceed
+- DEDUPLICATION: The create_vulnerability_report tool uses LLM-based deduplication. If it rejects your report as a duplicate, DO NOT attempt to re-submit the same vulnerability. Accept the rejection and move on to testing other areas. The vulnerability has already been reported by another agent
 </execution_guidelines>
 
 <vulnerability_focus>