Add comprehensive documentation and unit tests

Documentation:
- Add detailed README files for all services (auth, character, database, launcher, packet, utils, world)
- Create API documentation for the database service with detailed endpoint specifications
- Document database schema and relationships
- Add service architecture overviews and configuration instructions

Unit Tests:
- Implement comprehensive test suite for database repositories (user, character, session)
- Add gRPC service tests for database interactions
- Create tests for packet service components (bufferpool, connection, packets)
- Add utility service tests (health check, logging, load balancer, redis cache, service discovery)
- Implement auth service user tests
- Add character service tests

Code Structure:
- Reorganize test files into a more consistent structure
- Create a dedicated tests crate for integration testing
- Add test helpers and mock implementations for easier testing

database-service/API.md

@@ -0,0 +1,229 @@
+# Database Service API Documentation
+
+This document provides detailed information about the gRPC API endpoints exposed by the Database Service.
+
+## UserService
+
+### GetUser
+
+Retrieves a user by their ID.
+
+**Request:**
+```protobuf
+message GetUserRequest {
+  int32 user_id = 1;
+}
+```
+
+**Response:**
+```protobuf
+message GetUserResponse {
+  int32 user_id = 1;
+  string username = 2;
+  string email = 3;
+  string role = 4;
+}
+```
+
+**Error Codes:**
+- `NOT_FOUND`: User with the specified ID does not exist
+
+### GetUserByUsername
+
+Retrieves a user by their username.
+
+**Request:**
+```protobuf
+message GetUserByUsernameRequest {
+  string username = 1;
+}
+```
+
+**Response:**
+```protobuf
+message GetUserResponse {
+  int32 user_id = 1;
+  string username = 2;
+  string email = 3;
+  string role = 4;
+}
+```
+
+**Error Codes:**
+- `NOT_FOUND`: User with the specified username does not exist
+
+### GetUserByEmail
+
+Retrieves a user by their email address.
+
+**Request:**
+```protobuf
+message GetUserByEmailRequest {
+  string email = 1;
+}
+```
+
+**Response:**
+```protobuf
+message GetUserResponse {
+  int32 user_id = 1;
+  string username = 2;
+  string email = 3;
+  string role = 4;
+}
+```
+
+**Error Codes:**
+- `NOT_FOUND`: User with the specified email does not exist
+
+## CharacterDbService
+
+### GetCharacter
+
+Retrieves a character by ID.
+
+**Request:**
+```protobuf
+message CharacterRequest {
+  string user_id = 1;
+  int32 character_id = 2;
+}
+```
+
+**Response:**
+```protobuf
+message Character {
+  int32 id = 1;
+  string user_id = 2;
+  string name = 3;
+  int64 money = 4;
+  string inventory = 6;
+  string stats = 7;
+  string skills = 8;
+  string looks = 9;
+  string position = 10;
+  string created_at = 11;
+  string updated_at = 12;
+  string deleted_at = 13;
+  bool is_active = 14;
+}
+```
+
+**Error Codes:**
+- `NOT_FOUND`: Character with the specified ID does not exist
+
+### GetCharacterList
+
+Retrieves all characters for a user.
+
+**Request:**
+```protobuf
+message CharacterListRequest {
+  string user_id = 1;
+}
+```
+
+**Response:**
+```protobuf
+message CharacterListResponse {
+  repeated Character characters = 1;
+}
+```
+
+### CreateCharacter
+
+Creates a new character.
+
+**Request:**
+```protobuf
+message CreateCharacterRequest {
+  string user_id = 1;
+  string name = 2;
+  string inventory = 3; // JSON serialized
+  string skills = 4;    // JSON serialized
+  string stats = 5;     // JSON serialized
+  string looks = 6;     // JSON serialized
+  string position = 7;  // JSON serialized
+}
+```
+
+**Response:**
+```protobuf
+message CreateCharacterResponse {
+  int32 result = 1;
+  int32 character_id = 2;
+}
+```
+
+**Error Codes:**
+- `INTERNAL`: Failed to create character
+
+### DeleteCharacter
+
+Marks a character for deletion.
+
+**Request:**
+```protobuf
+message DeleteCharacterRequest {
+  string user_id = 1;
+  int32 character_id = 2;
+  int32 delete_type = 3;
+}
+```
+
+**Response:**
+```protobuf
+message DeleteCharacterResponse {
+  int64 remaining_time = 1;
+  string name = 2;
+}
+```
+
+**Error Codes:**
+- `INTERNAL`: Failed to delete character
+
+## SessionService
+
+### GetSession
+
+Retrieves session information.
+
+**Request:**
+```protobuf
+message GetSessionRequest {
+  string session_id = 1;
+}
+```
+
+**Response:**
+```protobuf
+message GetSessionResponse {
+  string session_id = 1;
+  string user_id = 2;
+}
+```
+
+**Error Codes:**
+- `NOT_FOUND`: Session with the specified ID does not exist
+
+### RefreshSession
+
+Updates session expiration.
+
+**Request:**
+```protobuf
+message RefreshSessionRequest {
+  string session_id = 1;
+}
+```
+
+**Response:**
+```protobuf
+message RefreshSessionResponse {
+  string session_id = 1;
+  string user_id = 2;
+}
+```
+
+**Error Codes:**
+- `NOT_FOUND`: Session with the specified ID does not exist