feat: Enhance admin user management system

- Add admin override capability to DELETE /api/auth/account endpoint
- Move /api/auth/users to admin-only with complete user fields (first_name, last_name, role, theme)
- Consolidate Bruno requests: remove duplicate List Users (Admin), merge Delete Account functionality
- Update all documentation to reflect enhanced capabilities
- Implement pgx 5 standards compliance with proper error handling

BREAKING CHANGES:
- /api/auth/users endpoint now requires admin role (was previously accessible)
- DELETE /api/auth/account accepts optional user_id parameter for admin deletion

cmd/server/main.go

@@ -70,10 +70,10 @@ func main() {
 	protected := e.Group("/api", jwtMiddleware)
 	protected.GET("/auth/profile", authHandler.GetProfile)
 	protected.PUT("/auth/profile", authHandler.UpdateProfile)
-	protected.GET("/auth/users", authHandler.ListUsers)
 
-	// Admin-only routes for folder management
+	// Admin-only routes for user and folder management
 	admin := protected.Group("/auth", handlers.AdminMiddleware)
+	admin.GET("/users", authHandler.ListUsers)
 	admin.POST("/ebook-folders", authHandler.AddEbookFolder)
 	admin.GET("/ebook-folders", authHandler.GetEbookFolders)
 	admin.DELETE("/ebook-folders", authHandler.DeleteEbookFolder)