Refactor and improve code consistency across multiple files

- Enhanced SQL queries in `session.go` and `share.go` for clarity and consistency.
- Updated comments for better understanding and maintenance.
- Ensured consistent error handling and return statements across various methods.

backend/internal/models/share.go

@@ -7,30 +7,30 @@ import (
 )
 
 type DocumentShare struct {
-    ID         uuid.UUID  `json:"id"`
-    DocumentID uuid.UUID  `json:"document_id"`
-    UserID     uuid.UUID  `json:"user_id"`
-    Permission string     `json:"permission"` // "view" or "edit"
-    CreatedAt  time.Time  `json:"created_at"`
-    CreatedBy  *uuid.UUID `json:"created_by"`
+	ID         uuid.UUID  `json:"id"`
+	DocumentID uuid.UUID  `json:"document_id"`
+	UserID     uuid.UUID  `json:"user_id"`
+	Permission string     `json:"permission"` // "view" or "edit"
+	CreatedAt  time.Time  `json:"created_at"`
+	CreatedBy  *uuid.UUID `json:"created_by"`
 }
 
 type CreateShareRequest struct {
-    UserEmail  string `json:"user_email" binding:"required"`
-    Permission string `json:"permission" binding:"required,oneof=view edit"`
+	UserEmail  string `json:"user_email" binding:"required"`
+	Permission string `json:"permission" binding:"required,oneof=view edit"`
 }
 
 type ShareListResponse struct {
-    Shares []DocumentShareWithUser `json:"shares"`
+	Shares []DocumentShareWithUser `json:"shares"`
 }
 
 type DocumentShareWithUser struct {
-    DocumentShare
-    User User `json:"user"`
+	DocumentShare
+	User User `json:"user"`
 }
 
 // PermissionResponse represents the user's permission level for a document
 type PermissionResponse struct {
-    Permission string `json:"permission"` // "view" or "edit"
-    Role       string `json:"role"`       // "owner", "editor", or "viewer"
+	Permission string `json:"permission"` // "view" or "edit"
+	Role       string `json:"role"`       // "owner", "editor", or "viewer"
 }