fix(jira): standalone tests as Sub-task under OFS-20798

OFS-20798 is a Task (child of OFS-20795 Epic), so tests nested
under it must be Sub-tasks, not Tasks — Task cannot parent Task.

Logic:
- parent_ticket_override (campaign) → Sub-task (unchanged)
- standalone_parent configured and differs from general parent → Sub-task
- only general parent (Epic) → Task

This fixes 'Please select valid parent issue' for standalone tests.

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

backend/app/services/jira_service.py

@@ -478,10 +478,22 @@ def auto_create_test_issue(
     try:
         jira = get_user_jira_client(actor, db)
 
-        # Tests nested under a campaign are Sub-tasks; standalone tests are Tasks
+        # Resolve parent and issue type together:
+        # - campaign parent override → Sub-task (Task cannot parent Task)
+        # - explicit standalone parent configured → Sub-task (same reason;
+        #   the standalone parent is a Task, e.g. OFS-20798)
+        # - only the general parent ticket (Epic) → Task
+        standalone_parent = get_jira_parent_ticket_standalone(db)
+        general_parent = get_jira_parent_ticket(db)
+        parent = parent_ticket_override or standalone_parent
+
+        has_explicit_parent = bool(
+            parent_ticket_override
+            or (standalone_parent and standalone_parent != general_parent)
+        )
         issue_type = (
             settings.JIRA_ISSUE_TYPE_SUBTASK
-            if parent_ticket_override
+            if has_explicit_parent
             else settings.JIRA_ISSUE_TYPE_TEST
         )
 
@@ -493,10 +505,6 @@ def auto_create_test_issue(
             "labels": ["aegis", "security-test", mitre_id.replace(".", "-")],
         }
 
-        # Use campaign ticket as parent when provided; otherwise use the
-        # standalone-tests parent (e.g. OFS-20798), falling back to the
-        # general parent ticket if the standalone one is not configured.
-        parent = parent_ticket_override or get_jira_parent_ticket_standalone(db)
         if parent:
             fields["parent"] = {"key": parent}