Categorize status fields as diagnostic

[CircuitSetup]

Summary

• categorize every active CT phase status as a diagnostic entity
• categorize the main board frequency status as a diagnostic entity
• apply the metadata consistently across the main board and all six add-on boards

Verification

• parsed all 7 status-field YAML files with yq
• confirmed all 43 active status fields have entity_category: diagnostic
• confirmed the branch contains exactly 43 metadata additions and no unrelated file changes