Add comprehensive human-readable comments to all Go files

- Comments explain what each function does and why
- Fixed unused strconv import in queue.go
- Better documentation for SMTP email service
- Explained journalctl log parsing in logs.go
- Clarified queue operations in queue.go

backend/internal/auth/rbac.go

@@ -1,18 +1,23 @@
 package auth
 
+// Role represents a user's role in the system.
 type Role string
 
+// Predefined roles.
 const (
-	RoleAdmin Role = "admin"
-	RoleUser  Role = "user"
+	RoleAdmin Role = "admin" // Full access to all features
+	RoleUser  Role = "user"  // Limited access (not currently used)
 )
 
+// Context holds the authenticated user's information.
+// This is stored in the request context during authentication.
 type Context struct {
-	UserID   uint
-	Username string
-	Role     Role
+	UserID   uint   // The user's database ID
+	Username string // The user's username for display
+	Role     Role   // The user's role (admin or user)
 }
 
+// IsAdmin checks if the user has admin privileges.
 func (c *Context) IsAdmin() bool {
 	return c.Role == RoleAdmin
 }