fix: correct YAML syntax in background_tasks rules

Fixed anti_patterns regex that used brackets inside single quotes,
which YAML interpreted as flow sequence syntax.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.architecture-rules/background_tasks.yaml

@@ -100,9 +100,9 @@ background_task_rules:
       - "error" -> "failed"
     severity: warning
     anti_patterns:
-      - pattern: 'status.*=.*["\']processing["\']'
+      - pattern: "status.*=.*processing"
         message: "Use 'running' instead of 'processing'"
-      - pattern: 'status.*=.*["\']fetching["\']'
+      - pattern: "status.*=.*fetching"
         message: "Use 'running' instead of 'fetching'"
     suggestion: |
       Use the standard status enum: