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/src/domain/services/IAggregateBoundaryDetector.ts

@@ -0,0 +1,45 @@
+import { AggregateBoundaryViolation } from "../value-objects/AggregateBoundaryViolation"
+
+/**
+ * Interface for detecting aggregate boundary violations in DDD
+ *
+ * Aggregate boundary violations occur when an entity from one aggregate
+ * directly references an entity from another aggregate. In DDD, aggregates
+ * should reference each other only by ID or Value Objects to maintain
+ * loose coupling and independence.
+ */
+export interface IAggregateBoundaryDetector {
+    /**
+     * Detects aggregate boundary violations in the given code
+     *
+     * Analyzes import statements to identify direct entity references
+     * across aggregate boundaries.
+     *
+     * @param code - Source code to analyze
+     * @param filePath - Path to the file being analyzed
+     * @param layer - The architectural layer of the file (should be 'domain')
+     * @returns Array of detected aggregate boundary violations
+     */
+    detectViolations(
+        code: string,
+        filePath: string,
+        layer: string | undefined,
+    ): AggregateBoundaryViolation[]
+
+    /**
+     * Checks if a file path belongs to an aggregate
+     *
+     * @param filePath - The file path to check
+     * @returns The aggregate name if found, undefined otherwise
+     */
+    extractAggregateFromPath(filePath: string): string | undefined
+
+    /**
+     * Checks if an import path references an entity from another aggregate
+     *
+     * @param importPath - The import path to analyze
+     * @param currentAggregate - The aggregate of the current file
+     * @returns True if the import crosses aggregate boundaries inappropriately
+     */
+    isAggregateBoundaryViolation(importPath: string, currentAggregate: string): boolean
+}