feat: add aggregate boundary validation (v0.7.0)

Implement DDD aggregate boundary validation to detect and prevent direct
entity references across aggregate boundaries.

Features:
- Detect direct entity imports between aggregates
- Allow only ID or Value Object references
- Support multiple folder structures (domain/aggregates/*, domain/*, domain/entities/*)
- Filter allowed imports (value-objects, events, repositories, services)
- Critical severity level for violations
- 41 comprehensive tests with 92.55% coverage
- CLI output with detailed suggestions
- Examples of good and bad patterns

Breaking changes: None
Backwards compatible: Yes

packages/guardian/examples/aggregate-boundary/bad/Order-DirectEntityReference.ts

@@ -0,0 +1,40 @@
+/**
+ * ❌ BAD EXAMPLE: Direct Entity Reference Across Aggregates
+ *
+ * Violation: Order aggregate directly imports and uses User entity from User aggregate
+ *
+ * Problems:
+ * 1. Creates tight coupling between aggregates
+ * 2. Changes to User entity affect Order aggregate
+ * 3. Violates aggregate boundary principles in DDD
+ * 4. Makes aggregates not independently modifiable
+ */
+
+import { User } from "../user/User"
+import { Product } from "../product/Product"
+
+export class Order {
+    private id: string
+    private user: User
+    private product: Product
+    private quantity: number
+
+    constructor(id: string, user: User, product: Product, quantity: number) {
+        this.id = id
+        this.user = user
+        this.product = product
+        this.quantity = quantity
+    }
+
+    getUserEmail(): string {
+        return this.user.email
+    }
+
+    getProductPrice(): number {
+        return this.product.price
+    }
+
+    calculateTotal(): number {
+        return this.product.price * this.quantity
+    }
+}

packages/guardian/examples/aggregate-boundary/good/Order-IdReference.ts

@@ -0,0 +1,40 @@
+/**
+ * ✅ GOOD EXAMPLE: Reference by ID
+ *
+ * Best Practice: Order aggregate references other aggregates only by their IDs
+ *
+ * Benefits:
+ * 1. Loose coupling between aggregates
+ * 2. Each aggregate can be modified independently
+ * 3. Follows DDD aggregate boundary principles
+ * 4. Clear separation of concerns
+ */
+
+import { UserId } from "../user/value-objects/UserId"
+import { ProductId } from "../product/value-objects/ProductId"
+
+export class Order {
+    private id: string
+    private userId: UserId
+    private productId: ProductId
+    private quantity: number
+
+    constructor(id: string, userId: UserId, productId: ProductId, quantity: number) {
+        this.id = id
+        this.userId = userId
+        this.productId = productId
+        this.quantity = quantity
+    }
+
+    getUserId(): UserId {
+        return this.userId
+    }
+
+    getProductId(): ProductId {
+        return this.productId
+    }
+
+    getQuantity(): number {
+        return this.quantity
+    }
+}

packages/guardian/examples/aggregate-boundary/good/Order-ValueObject.ts

@@ -0,0 +1,61 @@
+/**
+ * ✅ GOOD EXAMPLE: Using Value Objects for Needed Data
+ *
+ * Best Practice: When Order needs specific data from other aggregates,
+ * use Value Objects to store that data (denormalization)
+ *
+ * Benefits:
+ * 1. Order aggregate has all data it needs
+ * 2. No runtime dependency on other aggregates
+ * 3. Better performance (no joins needed)
+ * 4. Clear contract through Value Objects
+ */
+
+import { UserId } from "../user/value-objects/UserId"
+import { ProductId } from "../product/value-objects/ProductId"
+
+export class CustomerInfo {
+    constructor(
+        readonly customerId: UserId,
+        readonly customerName: string,
+        readonly customerEmail: string,
+    ) {}
+}
+
+export class ProductInfo {
+    constructor(
+        readonly productId: ProductId,
+        readonly productName: string,
+        readonly productPrice: number,
+    ) {}
+}
+
+export class Order {
+    private id: string
+    private customer: CustomerInfo
+    private product: ProductInfo
+    private quantity: number
+
+    constructor(id: string, customer: CustomerInfo, product: ProductInfo, quantity: number) {
+        this.id = id
+        this.customer = customer
+        this.product = product
+        this.quantity = quantity
+    }
+
+    getCustomerEmail(): string {
+        return this.customer.customerEmail
+    }
+
+    calculateTotal(): number {
+        return this.product.productPrice * this.quantity
+    }
+
+    getCustomerInfo(): CustomerInfo {
+        return this.customer
+    }
+
+    getProductInfo(): ProductInfo {
+        return this.product
+    }
+}