refactor: consolidate active identity migrations 004-006 into single migration

- Consolidate migrations 004, 005, and 006 into single 004_active_identity_management
- Remove redundant migrations 005 (constraint_fix) and 006 (settings_cleanup)
- Implement security-first approach with ON DELETE RESTRICT constraint from start
- Include comprehensive data migration from settings.activeDid to active_identity.activeDid
- Add proper cleanup of orphaned settings records and legacy activeDid values
- Update migrationService.ts validation logic to reflect consolidated structure
- Fix migration name references and enhance validation for hasBackedUpSeed column
- Reduce migration complexity from 3 separate operations to 1 atomic operation
- Maintain data integrity with foreign key constraints and performance indexes

Migration successfully tested on web platform with no data loss or corruption.
Active DID properly migrated: did:ethr:0xCA26A3959D32D2eB5459cE08203DbC4e62e79F5D

Files changed:
- src/db-sql/migration.ts: Consolidated 3 migrations into 1 (-46 lines)
- src/services/migrationService.ts: Updated validation logic (+13 lines)

src/db-sql/migration.ts

@@ -141,9 +141,11 @@ const MIGRATIONS = [
     `,
   },
   {
-    name: "004_active_identity_and_seed_backup",
+    name: "004_active_identity_management",
     sql: `
-      -- Migration 004: active_identity_and_seed_backup
+      -- Migration 004: active_identity_management (CONSOLIDATED)
+      -- Combines original migrations 004, 005, and 006 into single atomic operation
+      -- CRITICAL SECURITY: Uses ON DELETE RESTRICT constraint from the start
       -- Assumes master code deployed with migration 003 (hasBackedUpSeed)
       
       -- Enable foreign key constraints for data integrity
@@ -152,12 +154,12 @@ const MIGRATIONS = [
       -- Add UNIQUE constraint to accounts.did for foreign key support
       CREATE UNIQUE INDEX IF NOT EXISTS idx_accounts_did_unique ON accounts(did);
       
-      -- Create active_identity table with foreign key constraint
+      -- Create active_identity table with SECURE constraint (ON DELETE RESTRICT)
+      -- This prevents accidental account deletion - critical security feature
       CREATE TABLE IF NOT EXISTS active_identity (
         id INTEGER PRIMARY KEY CHECK (id = 1),
-        activeDid TEXT DEFAULT NULL,  -- NULL instead of empty string
-        lastUpdated TEXT NOT NULL DEFAULT (datetime('now')),
-        FOREIGN KEY (activeDid) REFERENCES accounts(did) ON DELETE SET NULL
+        activeDid TEXT REFERENCES accounts(did) ON DELETE RESTRICT,
+        lastUpdated TEXT NOT NULL DEFAULT (datetime('now'))
       );
 
       -- Add performance indexes
@@ -175,45 +177,10 @@ const MIGRATIONS = [
           lastUpdated = datetime('now')
       WHERE id = 1 
       AND EXISTS (SELECT 1 FROM settings WHERE id = 1 AND activeDid IS NOT NULL AND activeDid != '');
-    `,
-  },
-  {
-    name: "005_active_identity_constraint_fix",
-    sql: `
-      -- Migration 005: Fix foreign key constraint to ON DELETE RESTRICT
-      -- CRITICAL SECURITY FIX: Prevents accidental account deletion
       
-      PRAGMA foreign_keys = ON;
-      
-      -- Recreate table with ON DELETE RESTRICT constraint (SECURITY FIX)
-      CREATE TABLE active_identity_new (
-        id INTEGER PRIMARY KEY CHECK (id = 1),
-        activeDid TEXT REFERENCES accounts(did) ON DELETE RESTRICT,
-        lastUpdated TEXT NOT NULL DEFAULT (datetime('now'))
-      );
-      
-      -- Copy existing data
-      INSERT INTO active_identity_new (id, activeDid, lastUpdated)
-      SELECT id, activeDid, lastUpdated FROM active_identity;
-      
-      -- Replace old table
-      DROP TABLE active_identity;
-      ALTER TABLE active_identity_new RENAME TO active_identity;
-      
-      -- Recreate indexes
-      CREATE UNIQUE INDEX IF NOT EXISTS idx_active_identity_single_record ON active_identity(id);
-    `,
-  },
-  {
-    name: "006_settings_cleanup",
-    sql: `
-      -- Migration 006: Settings cleanup
-      -- Remove orphaned settings records and clear legacy activeDid values
-      
-      -- Remove orphaned settings records (accountDid is null)
+      -- CLEANUP: Remove orphaned settings records and clear legacy activeDid values
+      -- This completes the migration from settings-based to table-based active identity
       DELETE FROM settings WHERE accountDid IS NULL;
-      
-      -- Clear any remaining activeDid values in settings
       UPDATE settings SET activeDid = NULL;
     `,
   },