feat(activeDid): complete API layer with minimal safe $accountSettings update

- Add minimal change to prioritize activeDid from active_identity table
- Maintain all existing complex logic and backward compatibility
- Update migration plan to reflect API layer completion

The $accountSettings method now uses the new active_identity table as primary
source while preserving all existing settings merging and fallback behavior.

src/utils/PlatformServiceMixin.ts

@@ -858,7 +858,7 @@ export const PlatformServiceMixin = {
           return defaults;
         }
 
-        // Determine which DID to use - try new active_identity table first, fallback to settings
+        // Determine which DID to use - prioritize new active_identity table, fallback to settings
         const activeIdentity = await this.$getActiveIdentity();
         const targetDid =
           did || activeIdentity.activeDid || defaultSettings.activeDid;
@@ -875,6 +875,11 @@ export const PlatformServiceMixin = {
           defaultSettings,
         );
 
+        // Ensure activeDid comes from new table when available
+        if (activeIdentity.activeDid) {
+          mergedSettings.activeDid = activeIdentity.activeDid;
+        }
+
         // FIXED: Remove forced override - respect user preferences
         // Only set default if no user preference exists
         if (