feat: implement Phase 3 participant self-management (stories 4.5, 6.1)

Implemented features:
- Story 4.5: View Participant List - participants can see other active participants
- Story 6.1: Update Profile - participants can edit name and gift ideas before matching
- Utility functions for state management and business logic
- Comprehensive unit and integration tests

New files:
- src/utils/participant.py - Business logic utilities
- src/templates/participant/profile_edit.html - Profile edit form
- tests/unit/test_participant_utils.py - Unit tests for utilities
- tests/integration/test_participant_list.py - Integration tests for participant list
- tests/integration/test_profile_update.py - Integration tests for profile updates

Modified files:
- src/routes/participant.py - Added dashboard participant list and profile edit route
- src/templates/participant/dashboard.html - Added participant list section and edit link
- src/forms/participant.py - Added ProfileUpdateForm
- src/app.py - Added participant.profile_edit to setup check exemptions
- tests/conftest.py - Added exchange_factory, participant_factory, auth_participant fixtures

All tests passing. Phase 3.3 (reminder preferences) and 3.4 (withdrawal) remain to be implemented.

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

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

src/templates/participant/dashboard.html

@@ -37,6 +37,28 @@
             <dd>{{ participant.gift_ideas }}</dd>
             {% endif %}
         </dl>
+
+        {% if can_edit_profile %}
+        <a href="{{ url_for('participant.profile_edit') }}">Edit Profile</a>
+        {% endif %}
+    </section>
+
+    <section>
+        <h2>Participants ({{ participant_count }})</h2>
+        {% if participants %}
+        <ul>
+            {% for p in participants %}
+            <li>
+                {{ p.name }}
+                {% if p.id == participant.id %}
+                <span class="badge">You</span>
+                {% endif %}
+            </li>
+            {% endfor %}
+        </ul>
+        {% else %}
+        <p>No other participants yet. Share the registration link!</p>
+        {% endif %}
     </section>
 
     <section>

src/templates/participant/profile_edit.html

@@ -0,0 +1,64 @@
+{% extends "layouts/base.html" %}
+
+{% block title %}Edit Profile - {{ exchange.name }}{% endblock %}
+
+{% block content %}
+<article>
+    <header>
+        <h1>Edit Your Profile</h1>
+        <p>Update your display name and gift ideas. Your Secret Santa will see this information after matching.</p>
+    </header>
+
+    <form method="POST" action="{{ url_for('participant.profile_edit') }}">
+        {{ form.hidden_tag() }}
+
+        <div>
+            {{ form.name.label }}
+            {{ form.name(class="form-control") }}
+            {% if form.name.errors %}
+            <ul class="field-errors">
+                {% for error in form.name.errors %}
+                <li>{{ error }}</li>
+                {% endfor %}
+            </ul>
+            {% endif %}
+            <small>{{ form.name.description }}</small>
+        </div>
+
+        <div>
+            {{ form.gift_ideas.label }}
+            {{ form.gift_ideas(class="form-control") }}
+            {% if form.gift_ideas.errors %}
+            <ul class="field-errors">
+                {% for error in form.gift_ideas.errors %}
+                <li>{{ error }}</li>
+                {% endfor %}
+            </ul>
+            {% endif %}
+            <small>{{ form.gift_ideas.description }}</small>
+            <small id="gift-ideas-count">
+                {{ (form.gift_ideas.data or '')|length }} / 10,000 characters
+            </small>
+        </div>
+
+        <div>
+            <button type="submit">Save Changes</button>
+            <a href="{{ url_for('participant.dashboard', id=exchange.id) }}">Cancel</a>
+        </div>
+    </form>
+</article>
+
+<script>
+// Character counter (progressive enhancement)
+document.addEventListener('DOMContentLoaded', function() {
+    const textarea = document.querySelector('textarea[name="gift_ideas"]');
+    const counter = document.getElementById('gift-ideas-count');
+
+    if (textarea && counter) {
+        textarea.addEventListener('input', function() {
+            counter.textContent = this.value.length + ' / 10,000 characters';
+        });
+    }
+});
+</script>
+{% endblock %}