fix(activeDid): implement dual-write pattern with proper MASTER_SETTINGS_KEY usage

- Fix $updateActiveDid() to use MASTER_SETTINGS_KEY constant instead of hardcoded "1"
- Update migration plan to reflect current state after rollback
- Ensure backward compatibility during activeDid migration transition

The dual-write pattern now correctly updates both active_identity and settings tables
using the proper MASTER_SETTINGS_KEY constant for settings table targeting.

.cursor/rules/core/less_complex.mdc

@@ -12,6 +12,7 @@ language: Match repository languages and conventions
 
 ## Rules
 
+0. **Principle:** just the facts m'am.
 1. **Default to the least complex solution.** Fix the problem directly
    where it occurs; avoid new layers, indirection, or patterns unless
    strictly necessary.