✨ feat: implement user authentication system with JWT and PostgreSQL

Added comprehensive user management system:
- User registration with validation (3-50 char username, 6+ char password)
- JWT-based authentication with bcrypt password hashing
- Admin authentication with master password
- Password reset workflow with admin flagging
- PostgreSQL repository implementation
- SQLite repository for testing
- Unified authentication service interface

API Endpoints:
- POST /api/v1/auth/register - User registration
- POST /api/v1/auth/login - User/admin authentication
- POST /api/v1/auth/password-reset/request - Request password reset
- POST /api/v1/auth/password-reset/complete - Complete password reset
- POST /api/v1/auth/validate - JWT token validation

Security Features:
- Password hashing with bcrypt
- JWT token generation and validation
- Admin claims in JWT tokens
- Configurable token expiration
- Input validation for all endpoints

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

config.yaml

@@ -1,4 +1,4 @@
-# DanceLessonsCoach Configuration
+# dance-lessons-coach Configuration
 # This file serves as both the default configuration and documentation
 # All available options are shown with their default values
 
@@ -41,8 +41,8 @@ telemetry:
   # Format: host:port
   otlp_endpoint: "localhost:4317"
   
-  # Service name for tracing (default: "DanceLessonsCoach")
-  service_name: "DanceLessonsCoach"
+  # Service name for tracing (default: "dance-lessons-coach")
+  service_name: "dance-lessons-coach"
   
   # Use insecure connection (no TLS) (default: true)
   insecure: true
@@ -55,4 +55,36 @@ telemetry:
     
     # Sampling ratio (0.0 to 1.0, default: 1.0)
     # Only used with traceidratio and parentbased_traceidratio samplers
-    ratio: 1.0
+    ratio: 1.0
+
+# Database configuration (PostgreSQL)
+database:
+  # PostgreSQL host address (default: "localhost")
+  host: "localhost"
+  
+  # PostgreSQL port (default: 5432)
+  port: 5432
+  
+  # PostgreSQL username (default: "postgres")
+  user: "postgres"
+  
+  # PostgreSQL password (default: "postgres")
+  # Change this for production!
+  password: "postgres"
+  
+  # Database name (default: "dance_lessons_coach")
+  name: "dance_lessons_coach"
+  
+  # SSL mode (default: "disable")
+  # Options: "disable", "allow", "prefer", "require", "verify-ca", "verify-full"
+  ssl_mode: "disable"
+  
+  # Maximum number of open connections (default: 25)
+  max_open_conns: 25
+  
+  # Maximum number of idle connections (default: 5)
+  max_idle_conns: 5
+  
+  # Maximum lifetime of connections (default: "1h")
+  # Format: number + unit (s, m, h)
+  conn_max_lifetime: 1h