feat: add parent PIN setup functionality and email notifications

- Implemented User model updates to include PIN and related fields.
- Created email sender utility for sending verification and reset emails.
- Developed ParentPinSetup component for setting up a parent PIN with verification code.
- Enhanced UserProfile and EntityEditForm components to support new features.
- Updated routing to include PIN setup and authentication checks.
- Added styles for new components and improved existing styles for consistency.
- Introduced loading states and error handling in various components.

backend/utils/email_sender.py

@@ -0,0 +1,65 @@
+import os
+from flask import current_app
+from flask_mail import Mail, Message
+import smtplib
+from email.mime.text import MIMEText
+
+class EmailSender:
+    def __init__(self, app=None):
+        self.mail = None
+        if app is not None:
+            self.init_app(app)
+
+    def init_app(self, app):
+        self.mail = Mail(app)
+
+    def send_verification_email(self, to_email, token):
+        verify_url = f"{current_app.config['FRONTEND_URL']}/auth/verify?token={token}"
+        html_body = f'Click <a href="{verify_url}">here</a> to verify your account.'
+        msg = Message(
+            subject="Verify your account",
+            recipients=[to_email],
+            html=html_body,
+            sender=current_app.config.get('MAIL_DEFAULT_SENDER', 'no-reply@reward-app.local')
+        )
+        if self.mail:
+            self.mail.send(msg)
+        else:
+            print(f"[EMAIL to {to_email}] Verification: {verify_url}")
+
+    def send_reset_password_email(self, to_email, token):
+        reset_url = f"{current_app.config['FRONTEND_URL']}/auth/reset-password?token={token}"
+        html_body = f'Click <a href="{reset_url}">here</a> to reset your password.'
+        msg = Message(
+            subject="Reset your password",
+            recipients=[to_email],
+            html=html_body,
+            sender=current_app.config.get('MAIL_DEFAULT_SENDER', 'no-reply@reward-app.local')
+        )
+        if self.mail:
+            self.mail.send(msg)
+        else:
+            print(f"[EMAIL to {to_email}] Reset password: {reset_url}")
+
+    def send_pin_setup_email(self, to_email, code):
+        html_body = f"""
+        <div style='font-family:sans-serif;'>
+          <h2>Set up your Parent PIN</h2>
+          <p>To set your Parent PIN, enter the following code in the app:</p>
+          <div style='font-size:2rem; font-weight:bold; letter-spacing:0.2em; margin:1.5rem 0;'>{code}</div>
+          <p>This code is valid for 10 minutes.</p>
+          <p>If you did not request this, you can ignore this email.</p>
+          <hr>
+          <div style='color:#888;font-size:0.95rem;'>Reward App</div>
+        </div>
+        """
+        msg = Message(
+            subject="Set up your Parent PIN",
+            recipients=[to_email],
+            html=html_body,
+            sender=current_app.config.get('MAIL_DEFAULT_SENDER', 'no-reply@reward-app.local')
+        )
+        if self.mail:
+            self.mail.send(msg)
+        else:
+            print(f"[EMAIL to {to_email}] Parent PIN setup code: {code}")