Add email verification, admin approval, and user profile enhancements

Implement comprehensive email verification and admin approval system for user registration. Users must verify their email before logging in, and admins must approve new users before they can access the system.

Major features:
- Email verification with UUID tokens (24hr expiry, one-time use)
- Admin approval workflow via Django admin interface
- Custom authentication backend enforcing verification and approval
- Password change functionality for authenticated users
- Enhanced profile page with proper styling and theme support
- Collect first name, last name, and timezone during registration
- Profile link added to header navigation

Email notifications:
- Verification email sent after registration
- Admin notification when users need approval
- Approval notification sent to users

Security features:
- Cryptographically secure UUID tokens
- Token expiration and one-time use enforcement
- Email enumeration protection
- Custom JWT token validation for API access
- Existing users auto-approved via data migration

Templates added:
- Email templates (verification, approval, admin notification)
- Web templates (password change, verification pages)
- Enhanced profile page with dark/light mode support

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

templates/users/register_success.html

@@ -0,0 +1,40 @@
+{% extends "base.html" %}
+
+{% block title %}Registration Successful - KeepItGoing{% endblock %}
+
+{% block body %}
+<div style="min-height: 100vh; display: flex; align-items: center; justify-content: center; background-color: var(--color-bg, #f5f5f5); padding: 20px;">
+    <div style="max-width: 500px; width: 100%; background: white; padding: 40px; border-radius: 8px; box-shadow: 0 2px 10px rgba(0,0,0,0.1);">
+        <div style="text-align: center; margin-bottom: 30px;">
+            <svg style="width: 80px; height: 80px; color: #10B981;" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M3 19v-8.93a2 2 0 01.89-1.664l7-4.666a2 2 0 012.22 0l7 4.666A2 2 0 0121 10.07V19M3 19a2 2 0 002 2h14a2 2 0 002-2M3 19l6.75-4.5M21 19l-6.75-4.5M3 10l6.75 4.5M21 10l-6.75 4.5m0 0l-1.14.76a2 2 0 01-2.22 0l-1.14-.76"></path>
+            </svg>
+        </div>
+
+        <h2 style="text-align: center; color: #2c3e50; margin-bottom: 20px;">Check Your Email!</h2>
+
+        <p style="text-align: center; color: #666; margin-bottom: 15px;">
+            We've sent a verification email to:
+        </p>
+        <p style="text-align: center; font-weight: bold; color: #2c3e50; margin-bottom: 20px;">
+            {{ email }}
+        </p>
+
+        <p style="color: #666; margin-bottom: 15px;">
+            Please click the link in the email to verify your account. After verification,
+            your account will be reviewed by our team for approval.
+        </p>
+
+        <div style="background-color: #e3f2fd; padding: 15px; border-radius: 5px; margin-top: 30px;">
+            <p style="margin: 0; color: #0d47a1; font-size: 14px;">
+                <strong>Didn't receive the email?</strong><br>
+                Check your spam folder or <a href="{% url 'resend-verification' %}" style="color: #1976d2; text-decoration: none; font-weight: bold;">request a new verification email</a>.
+            </p>
+        </div>
+
+        <div style="text-align: center; margin-top: 30px;">
+            <a href="{% url 'login' %}" style="color: #666; text-decoration: none; font-size: 14px;">Return to Login</a>
+        </div>
+    </div>
+</div>
+{% endblock %}