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.

src/utils/PlatformServiceMixin.ts

@@ -219,8 +219,9 @@ export const PlatformServiceMixin = {
             "UPDATE active_identity SET activeDid = ?, lastUpdated = datetime('now') WHERE id = 1",
             [newDid || ""],
           );
-          await this.$dbExec("UPDATE settings SET activeDid = ? WHERE id = 1", [
+          await this.$dbExec("UPDATE settings SET activeDid = ? WHERE id = ?", [
             newDid || "",
+            MASTER_SETTINGS_KEY,
           ]);
           logger.debug(
             `[PlatformServiceMixin] ActiveDid dual-write completed for ${newDid}`,