Add REST API tools: client library, auth filter, validation, and tests

[devin-ai-integration]

Summary

Adds a complete set of reusable REST API tools to the petstore project:

1. REST API Client (io.swagger.petstore.client)

• PetStoreClient — typed HTTP client wrapping all petstore endpoints (Pet, Store, User CRUD) with built-in API key auth, configurable timeouts, and ApiResponse<T> wrapper for status/body inspection
• ApiClientConfig — builder-pattern configuration for base URL, API key, timeouts

PetStoreClient client = new PetStoreClient("http://localhost:8080/api/v3", "special-key");
ApiResponse<Pet> resp = client.getPetById(1L, Pet.class);

2. Authentication/Authorization (io.swagger.petstore.security)

• ApiKeyAuthFilter — servlet filter validating api_key header, Authorization: Bearer, or query param; skips public endpoints (login, logout, openapi spec, OPTIONS)
• ApiKeyStore — singleton in-memory key registry (production: swap for DB lookup)
• SecurityContext — models OAuth2 scopes (read:pets, write:pets) for future use

3. Request Validation (io.swagger.petstore.validation)

• RequestValidator — static validators for Pet (name required, status enum, photoUrls non-empty), Order (petId > 0, quantity > 0, status enum), User (username required, email/phone format)
• ValidationResult — immutable error list with isValid(), getErrorMessage()

4. Tests — 74 unit tests across controllers, validation, client config, and security (JUnit 4 + Mockito)

5. Documentation — docs/API_TOOLS.md with usage examples, curl commands, and architecture overview

Dependencies added (pom.xml): JUnit 4.13.2 (test), Mockito 4.11.0 (test), javax.servlet-api 3.1.0 (provided)

Link to Devin session: https://partner-workshops.devinenterprise.com/sessions/c056fa75403a48eb86b94db3429c5598

[devin-ai-integration]

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