fix(jira): remove priority field from issue creation — OFS project has non-standard priorities

The OFS Jira project does not have the default Jira priority scheme
(Highest/High/Medium/Low/Lowest), causing a 'priority selected is invalid'
error on every ticket creation. Removing the priority field lets Jira use
the project default.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/services/jira_service.py

@@ -472,7 +472,6 @@ def auto_create_test_issue(
             "summary": f"[Aegis] {mitre_id} — {test.name}",
             "description": _build_test_description(test, technique),
             "issuetype": {"name": settings.JIRA_ISSUE_TYPE_TEST},
-            "priority": {"name": _SEVERITY_TO_PRIORITY.get(severity, "Medium")},
             "labels": ["aegis", "security-test", mitre_id.replace(".", "-")],
         }