feat: Implement email change functionality

This commit introduces the following changes:

-   Added new API endpoints for email change requests and
    verification.
-   Updated the backend code to support email change workflow,
    including validation, code generation, and email sending.
-   Updated the frontend to include components for initiating and
    verifying email changes.
-   Added new dependencies to support email change functionality.
-   Updated the existing components to include email change
    functionality.

https://codeberg.org/mapleopentech/monorepo/issues/1

cloud/maplefile-backend/internal/domain/user/model.go

@@ -121,6 +121,11 @@ type UserSecurityData struct {
 
 	// OTPBackupCodeHashAlgorithm tracks the hashing algorithm used.
 	OTPBackupCodeHashAlgorithm string `bson:"otp_backup_code_hash_algorithm" json:"-"`
+
+	// Email change verification fields
+	PendingEmail       string    `bson:"pending_email,omitempty" json:"pending_email,omitempty"`             // New email pending verification
+	PendingEmailCode   string    `bson:"pending_email_code,omitempty" json:"pending_email_code,omitempty"`   // Verification code for new email (sensitive, stored internally but never exposed in API responses)
+	PendingEmailExpiry time.Time `bson:"pending_email_expiry,omitempty" json:"pending_email_expiry,omitempty"` // When verification expires
 }
 
 type UserMetadata struct {