feat: implement Story 4.1 - Access Registration Page

Allows potential participants to view exchange details and access
the registration form via unique slug URLs.

Implementation:
- Added ParticipantRegistrationForm with name, email, gift_ideas, and reminder fields
- Created GET /exchange/<slug>/register route
- Built responsive registration template with exchange details
- Exempted participant routes from admin setup requirement
- Comprehensive test coverage for all scenarios

Acceptance Criteria Met:
- Valid slug displays registration form with exchange details
- Invalid slug returns 404
- Form includes all required fields with CSRF protection
- Registration deadline is displayed

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

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

src/forms/__init__.py

@@ -2,6 +2,7 @@
 
 from src.forms.exchange import ExchangeForm
 from src.forms.login import LoginForm
+from src.forms.participant import ParticipantRegistrationForm
 from src.forms.setup import SetupForm
 
-__all__ = ["ExchangeForm", "LoginForm", "SetupForm"]
+__all__ = ["ExchangeForm", "LoginForm", "ParticipantRegistrationForm", "SetupForm"]

src/forms/participant.py

@@ -0,0 +1,37 @@
+"""Forms for participant registration and management."""
+
+from flask_wtf import FlaskForm
+from wtforms import BooleanField, EmailField, StringField, TextAreaField
+from wtforms.validators import DataRequired, Email, Length
+
+
+class ParticipantRegistrationForm(FlaskForm):
+    """Form for participant registration."""
+
+    name = StringField(
+        "Name",
+        validators=[
+            DataRequired(message="Name is required"),
+            Length(max=255, message="Name must be less than 255 characters"),
+        ],
+    )
+
+    email = EmailField(
+        "Email",
+        validators=[
+            DataRequired(message="Email is required"),
+            Email(message="Please enter a valid email address"),
+            Length(max=255, message="Email must be less than 255 characters"),
+        ],
+    )
+
+    gift_ideas = TextAreaField(
+        "Gift Ideas",
+        description="Optional: Share ideas to help your Secret Santa",
+    )
+
+    reminder_enabled = BooleanField(
+        "Send me reminders",
+        default=True,
+        description="Receive email reminders about important dates",
+    )