feat: add dependency direction enforcement (v0.4.0)

Implement dependency direction detection to enforce Clean Architecture rules:
- Domain layer can only import from Domain and Shared
- Application layer can only import from Domain, Application, and Shared
- Infrastructure layer can import from all layers
- Shared layer can be imported by all layers

Added:
- IDependencyDirectionDetector interface in domain layer
- DependencyViolation value object with detailed suggestions and examples
- DependencyDirectionDetector implementation in infrastructure
- Integration with AnalyzeProject use case
- New DEPENDENCY_DIRECTION rule in constants
- 43 comprehensive tests covering all scenarios (100% passing)
- Good and bad examples in examples directory

Improvements:
- Optimized extractLayerFromImport method to reduce complexity
- Fixed indentation in DependencyGraph.ts
- Updated getExampleFix to avoid false positives in old detector

Test Results:
- All 261 tests passing
- Build successful
- Self-check: 0 architecture violations in src code

packages/guardian/src/domain/entities/DependencyGraph.ts

@@ -94,7 +94,7 @@ export class DependencyGraph extends BaseEntity {
         totalDependencies: number
         avgDependencies: number
         maxDependencies: number
-    } {
+        } {
         const nodes = Array.from(this.nodes.values())
         const totalFiles = nodes.length
         const totalDependencies = nodes.reduce((sum, node) => sum + node.dependencies.length, 0)

packages/guardian/src/domain/services/IDependencyDirectionDetector.ts

@@ -0,0 +1,47 @@
+import { DependencyViolation } from "../value-objects/DependencyViolation"
+
+/**
+ * Interface for detecting dependency direction violations in the codebase
+ *
+ * Dependency direction violations occur when a layer imports from a layer
+ * that it should not depend on according to Clean Architecture principles:
+ * - Domain should not import from Application or Infrastructure
+ * - Application should not import from Infrastructure
+ * - Infrastructure can import from Application and Domain
+ * - Shared can be imported by all layers
+ */
+export interface IDependencyDirectionDetector {
+    /**
+     * Detects dependency direction violations in the given code
+     *
+     * Analyzes import statements to identify violations of dependency rules
+     * between architectural layers.
+     *
+     * @param code - Source code to analyze
+     * @param filePath - Path to the file being analyzed
+     * @param layer - The architectural layer of the file (domain, application, infrastructure, shared)
+     * @returns Array of detected dependency direction violations
+     */
+    detectViolations(
+        code: string,
+        filePath: string,
+        layer: string | undefined,
+    ): DependencyViolation[]
+
+    /**
+     * Checks if an import violates dependency direction rules
+     *
+     * @param fromLayer - The layer that is importing
+     * @param toLayer - The layer being imported
+     * @returns True if the import violates dependency rules
+     */
+    isViolation(fromLayer: string, toLayer: string): boolean
+
+    /**
+     * Extracts the layer from an import path
+     *
+     * @param importPath - The import path to analyze
+     * @returns The layer name if detected, undefined otherwise
+     */
+    extractLayerFromImport(importPath: string): string | undefined
+}

packages/guardian/src/domain/value-objects/DependencyViolation.ts

@@ -0,0 +1,162 @@
+import { ValueObject } from "./ValueObject"
+
+interface DependencyViolationProps {
+    readonly fromLayer: string
+    readonly toLayer: string
+    readonly importPath: string
+    readonly filePath: string
+    readonly line?: number
+}
+
+/**
+ * Represents a dependency direction violation in the codebase
+ *
+ * Dependency direction violations occur when a layer imports from a layer
+ * that it should not depend on according to Clean Architecture principles:
+ * - Domain → should not import from Application or Infrastructure
+ * - Application → should not import from Infrastructure
+ * - Infrastructure → can import from Application and Domain (allowed)
+ * - Shared → can be imported by all layers (allowed)
+ *
+ * @example
+ * ```typescript
+ * // Bad: Domain importing from Application
+ * const violation = DependencyViolation.create(
+ *     'domain',
+ *     'application',
+ *     '../../application/dtos/UserDto',
+ *     'src/domain/entities/User.ts',
+ *     5
+ * )
+ *
+ * console.log(violation.getMessage())
+ * // "Domain layer should not import from Application layer"
+ * ```
+ */
+export class DependencyViolation extends ValueObject<DependencyViolationProps> {
+    private constructor(props: DependencyViolationProps) {
+        super(props)
+    }
+
+    public static create(
+        fromLayer: string,
+        toLayer: string,
+        importPath: string,
+        filePath: string,
+        line?: number,
+    ): DependencyViolation {
+        return new DependencyViolation({
+            fromLayer,
+            toLayer,
+            importPath,
+            filePath,
+            line,
+        })
+    }
+
+    public get fromLayer(): string {
+        return this.props.fromLayer
+    }
+
+    public get toLayer(): string {
+        return this.props.toLayer
+    }
+
+    public get importPath(): string {
+        return this.props.importPath
+    }
+
+    public get filePath(): string {
+        return this.props.filePath
+    }
+
+    public get line(): number | undefined {
+        return this.props.line
+    }
+
+    public getMessage(): string {
+        return `${this.capitalizeFirst(this.props.fromLayer)} layer should not import from ${this.capitalizeFirst(this.props.toLayer)} layer`
+    }
+
+    public getSuggestion(): string {
+        const suggestions: string[] = []
+
+        if (this.props.fromLayer === "domain") {
+            suggestions.push(
+                "Domain layer should be independent and not depend on other layers",
+                "Move the imported code to the domain layer if it contains business logic",
+                "Use dependency inversion: define an interface in domain and implement it in infrastructure",
+            )
+        } else if (this.props.fromLayer === "application") {
+            suggestions.push(
+                "Application layer should not depend on infrastructure",
+                "Define an interface (Port) in application layer",
+                "Implement the interface (Adapter) in infrastructure layer",
+                "Use dependency injection to provide the implementation",
+            )
+        }
+
+        return suggestions.join("\n")
+    }
+
+    public getExampleFix(): string {
+        if (this.props.fromLayer === "domain" && this.props.toLayer === "infrastructure") {
+            return `
+// ❌ Bad: Domain depends on Infrastructure (PrismaClient)
+// domain/services/UserService.ts
+class UserService {
+    constructor(private prisma: PrismaClient) {}
+}
+
+// ✅ Good: Domain defines interface, Infrastructure implements
+// domain/repositories/IUserRepository.ts
+interface IUserRepository {
+    findById(id: UserId): Promise<User | null>
+    save(user: User): Promise<void>
+}
+
+// domain/services/UserService.ts
+class UserService {
+    constructor(private userRepo: IUserRepository) {}
+}
+
+// infrastructure/repositories/PrismaUserRepository.ts
+class PrismaUserRepository implements IUserRepository {
+    constructor(private prisma: PrismaClient) {}
+    async findById(id: UserId): Promise<User | null> { }
+    async save(user: User): Promise<void> { }
+}`
+        }
+
+        if (this.props.fromLayer === "application" && this.props.toLayer === "infrastructure") {
+            return `
+// ❌ Bad: Application depends on Infrastructure (SmtpEmailService)
+// application/use-cases/SendEmail.ts
+class SendWelcomeEmail {
+    constructor(private emailService: SmtpEmailService) {}
+}
+
+// ✅ Good: Application defines Port, Infrastructure implements Adapter
+// application/ports/IEmailService.ts
+interface IEmailService {
+    send(to: string, subject: string, body: string): Promise<void>
+}
+
+// application/use-cases/SendEmail.ts
+class SendWelcomeEmail {
+    constructor(private emailService: IEmailService) {}
+}
+
+// infrastructure/adapters/SmtpEmailService.ts
+class SmtpEmailService implements IEmailService {
+    async send(to: string, subject: string, body: string): Promise<void> { }
+}`
+        }
+
+        return ""
+    }
+
+    private capitalizeFirst(str: string): string {
+        return str.charAt(0).toUpperCase() + str.slice(1)
+    }
+}