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
+    }
+}