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/examples/good-architecture/dependency-direction/GoodApplicationLayer.ts

@@ -0,0 +1,91 @@
+/**
+ * ✅ GOOD: Application layer with correct dependencies
+ *
+ * Application should only import from:
+ * - Domain layer
+ * - Other application files
+ * - Shared utilities
+ *
+ * Application should NOT import from:
+ * - Infrastructure layer
+ */
+
+import { User } from "../domain/entities/User"
+import { Email } from "../domain/value-objects/Email"
+import { UserId } from "../domain/value-objects/UserId"
+import { IUserRepository } from "../domain/repositories/IUserRepository"
+import { Result } from "../../../src/shared/types/Result"
+
+/**
+ * ✅ Use case depends on domain interfaces (IUserRepository)
+ * NOT on infrastructure implementations
+ */
+export class CreateUser {
+    constructor(private readonly userRepo: IUserRepository) {}
+
+    async execute(request: CreateUserRequest): Promise<Result<UserResponseDto>> {
+        const emailResult = Email.create(request.email)
+        if (emailResult.isFailure) {
+            return Result.fail(emailResult.error)
+        }
+
+        const userId = UserId.generate()
+        const user = new User(userId, emailResult.value)
+
+        await this.userRepo.save(user)
+
+        return Result.ok(UserMapper.toDto(user))
+    }
+}
+
+/**
+ * ✅ DTO in application layer
+ */
+export interface CreateUserRequest {
+    email: string
+    name: string
+}
+
+export interface UserResponseDto {
+    id: string
+    email: string
+    createdAt: string
+}
+
+/**
+ * ✅ Mapper in application layer converting domain to DTO
+ */
+export class UserMapper {
+    static toDto(user: User): UserResponseDto {
+        return {
+            id: user.getId().getValue(),
+            email: user.getEmail().getValue(),
+            createdAt: user.getCreatedAt().toISOString(),
+        }
+    }
+}
+
+/**
+ * ✅ Application defines Port (interface) for email service
+ * Infrastructure will provide the Adapter (implementation)
+ */
+export interface IEmailService {
+    sendWelcomeEmail(email: string): Promise<void>
+}
+
+export class SendWelcomeEmail {
+    constructor(
+        private readonly userRepo: IUserRepository,
+        private readonly emailService: IEmailService,
+    ) {}
+
+    async execute(userId: string): Promise<Result<void>> {
+        const user = await this.userRepo.findById(UserId.from(userId))
+        if (!user) {
+            return Result.fail("User not found")
+        }
+
+        await this.emailService.sendWelcomeEmail(user.getEmail().getValue())
+        return Result.ok()
+    }
+}

packages/guardian/examples/good-architecture/dependency-direction/GoodDomainLayer.ts

@@ -0,0 +1,56 @@
+/**
+ * ✅ GOOD: Domain layer with correct dependencies
+ *
+ * Domain should only import from:
+ * - Other domain files
+ * - Shared utilities
+ *
+ * Domain should NOT import from:
+ * - Application layer
+ * - Infrastructure layer
+ */
+
+import { Email } from "../domain/value-objects/Email"
+import { UserId } from "../domain/value-objects/UserId"
+import { Result } from "../../../src/shared/types/Result"
+
+/**
+ * ✅ Domain entity using only domain value objects and shared types
+ */
+export class User {
+    private readonly id: UserId
+    private email: Email
+    private readonly createdAt: Date
+
+    constructor(id: UserId, email: Email, createdAt: Date = new Date()) {
+        this.id = id
+        this.email = email
+        this.createdAt = createdAt
+    }
+
+    public getId(): UserId {
+        return this.id
+    }
+
+    public getEmail(): Email {
+        return this.email
+    }
+
+    public changeEmail(newEmail: Email): Result<void> {
+        if (this.email.equals(newEmail)) {
+            return Result.fail("Email is the same")
+        }
+
+        this.email = newEmail
+        return Result.ok()
+    }
+}
+
+/**
+ * ✅ Domain repository interface (not importing from infrastructure)
+ */
+export interface IUserRepository {
+    findById(id: UserId): Promise<User | null>
+    save(user: User): Promise<void>
+    delete(id: UserId): Promise<void>
+}

packages/guardian/examples/good-architecture/dependency-direction/GoodInfrastructureLayer.ts

@@ -0,0 +1,128 @@
+/**
+ * ✅ GOOD: Infrastructure layer with correct dependencies
+ *
+ * Infrastructure CAN import from:
+ * - Domain layer
+ * - Application layer
+ * - Other infrastructure files
+ * - Shared utilities
+ * - External libraries (ORM, frameworks, etc.)
+ */
+
+import { User } from "../domain/entities/User"
+import { UserId } from "../domain/value-objects/UserId"
+import { Email } from "../domain/value-objects/Email"
+import { IUserRepository } from "../domain/repositories/IUserRepository"
+import { CreateUser } from "../application/use-cases/CreateUser"
+import { UserResponseDto } from "../application/dtos/UserResponseDto"
+import { IEmailService } from "../application/ports/IEmailService"
+
+/**
+ * ✅ Infrastructure implements domain interface
+ */
+export class InMemoryUserRepository implements IUserRepository {
+    private users: Map<string, User> = new Map()
+
+    async findById(id: UserId): Promise<User | null> {
+        return this.users.get(id.getValue()) ?? null
+    }
+
+    async save(user: User): Promise<void> {
+        this.users.set(user.getId().getValue(), user)
+    }
+
+    async delete(id: UserId): Promise<void> {
+        this.users.delete(id.getValue())
+    }
+}
+
+/**
+ * ✅ Infrastructure provides Adapter implementing application Port
+ */
+export class SmtpEmailService implements IEmailService {
+    constructor(
+        private readonly host: string,
+        private readonly port: number,
+    ) {}
+
+    async sendWelcomeEmail(email: string): Promise<void> {
+        console.log(`Sending welcome email to ${email} via SMTP`)
+    }
+}
+
+/**
+ * ✅ Controller uses application use cases and DTOs
+ */
+export class UserController {
+    constructor(private readonly createUser: CreateUser) {}
+
+    async create(request: { email: string; name: string }): Promise<UserResponseDto> {
+        const result = await this.createUser.execute(request)
+
+        if (result.isFailure) {
+            throw new Error(result.error)
+        }
+
+        return result.value
+    }
+}
+
+/**
+ * ✅ Infrastructure can use external frameworks
+ */
+import express from "express"
+
+export class ExpressServer {
+    private app = express()
+
+    constructor(private readonly userController: UserController) {
+        this.setupRoutes()
+    }
+
+    private setupRoutes(): void {
+        this.app.post("/users", async (req, res) => {
+            const user = await this.userController.create(req.body)
+            res.json(user)
+        })
+    }
+}
+
+/**
+ * ✅ Infrastructure can use ORM
+ */
+import { PrismaClient } from "@prisma/client"
+
+export class PrismaUserRepository implements IUserRepository {
+    constructor(private readonly prisma: PrismaClient) {}
+
+    async findById(id: UserId): Promise<User | null> {
+        const userData = await this.prisma.user.findUnique({
+            where: { id: id.getValue() },
+        })
+
+        if (!userData) {
+            return null
+        }
+
+        return new User(UserId.from(userData.id), Email.create(userData.email).value)
+    }
+
+    async save(user: User): Promise<void> {
+        await this.prisma.user.upsert({
+            where: { id: user.getId().getValue() },
+            create: {
+                id: user.getId().getValue(),
+                email: user.getEmail().getValue(),
+            },
+            update: {
+                email: user.getEmail().getValue(),
+            },
+        })
+    }
+
+    async delete(id: UserId): Promise<void> {
+        await this.prisma.user.delete({
+            where: { id: id.getValue() },
+        })
+    }
+}