refactor(db): restructure migrations to preserve master compatibility

- Split consolidated migration into 3 separate migrations
- Preserve master's 001_initial and 002_add_iViewContent structure
- Move active_identity creation to new 003_active_identity_and_seed_backup
- Add hasBackedUpSeed field from registration-prompt-parity branch
- Remove activeDid performance index for simplified migration
- Maintain foreign key constraints and smart deletion pattern
- Remove unused $getAllAccountDids method from PlatformServiceMixin

This restructure ensures backward compatibility with master branch
while adding advanced features (active_identity table, seed backup
tracking) in a clean, maintainable migration sequence.

src/utils/PlatformServiceMixin.ts

@@ -741,17 +741,6 @@ export const PlatformServiceMixin = {
     // SMART DELETION PATTERN DAL METHODS
     // =================================================
 
-    /**
-     * Get all account DIDs ordered by creation date
-     * Required for smart deletion pattern
-     */
-    async $getAllAccountDids(): Promise<string[]> {
-      const result = await this.$dbQuery(
-        "SELECT did FROM accounts ORDER BY dateCreated, did",
-      );
-      return result?.values?.map((row) => row[0] as string) || [];
-    },
-
     /**
      * Get account DID by ID
      * Required for smart deletion pattern