feat(db): add deletedAt audit timestamp to soft-deletable models

Add deletedAt DateTime? to User, Client, Role, Resource, and Blueprint
models for GDPR-compliant deactivation audit trail. Soft-delete mutations
now stamp deletedAt: new Date() on deactivation and clear it on
reactivation. Migration and test assertions updated accordingly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/db/prisma/migrations/20260409_add_deleted_at.sql

@@ -0,0 +1,5 @@
+ALTER TABLE "User" ADD COLUMN IF NOT EXISTS "deletedAt" TIMESTAMP(3);
+ALTER TABLE "Client" ADD COLUMN IF NOT EXISTS "deletedAt" TIMESTAMP(3);
+ALTER TABLE "Role" ADD COLUMN IF NOT EXISTS "deletedAt" TIMESTAMP(3);
+ALTER TABLE "Resource" ADD COLUMN IF NOT EXISTS "deletedAt" TIMESTAMP(3);
+ALTER TABLE "Blueprint" ADD COLUMN IF NOT EXISTS "deletedAt" TIMESTAMP(3);

packages/db/prisma/schema.prisma

@@ -188,6 +188,7 @@ model User {
   totpSecret         String?           // Base32 TOTP secret
   totpEnabled        Boolean  @default(false)
   isActive           Boolean  @default(true)
+  deletedAt          DateTime?
 
   accounts          Account[]
   sessions          Session[]
@@ -709,6 +710,7 @@ model Client {
   parent    Client?   @relation("ClientTree", fields: [parentId], references: [id])
   children  Client[]  @relation("ClientTree")
   isActive  Boolean   @default(true)
+  deletedAt DateTime?
   sortOrder Int       @default(0)
   tags      String[]  @default([])
 
@@ -771,6 +773,7 @@ model Blueprint {
   // rolePresets: StaffingRequirement[] — default roles for project creation wizard
   rolePresets     Json            @db.JsonB @default("[]")
   isActive        Boolean         @default(true)
+  deletedAt       DateTime?
   isGlobal        Boolean         @default(false)
 
   resources       Resource[]
@@ -792,6 +795,7 @@ model Role {
   description   String?
   color         String?        // hex color e.g. "#6366f1"
   isActive      Boolean        @default(true)
+  deletedAt     DateTime?
 
   resourceRoles          ResourceRole[]
   demandRequirements     DemandRequirement[]
@@ -847,6 +851,7 @@ model Resource {
   blueprintId         String?
   blueprint           Blueprint? @relation(fields: [blueprintId], references: [id])
   isActive            Boolean   @default(true)
+  deletedAt           DateTime?
 
   userId              String?   @unique
   user                User?     @relation(fields: [userId], references: [id])