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>

tests/integration/test_participant_list.py

@@ -0,0 +1,135 @@
+"""Integration tests for participant list functionality."""
+
+from datetime import UTC, datetime
+
+from flask import url_for
+
+
+def test_participant_list_shows_all_active(
+    client, auth_participant, participant_factory
+):
+    """Test participant list shows all active participants."""
+    # auth_participant fixture creates session and one participant
+    exchange = auth_participant.exchange
+
+    # Create 2 more active participants
+    participant_factory(exchange=exchange, name="Bob")
+    participant_factory(exchange=exchange, name="Charlie")
+
+    response = client.get(url_for("participant.dashboard", id=exchange.id))
+
+    assert response.status_code == 200
+    assert b"Bob" in response.data
+    assert b"Charlie" in response.data
+    assert b"Participants (3)" in response.data
+
+
+def test_participant_list_excludes_withdrawn(
+    client, auth_participant, participant_factory
+):
+    """Test withdrawn participants are not shown."""
+    exchange = auth_participant.exchange
+
+    # Create active and withdrawn participants
+    participant_factory(exchange=exchange, name="Active")
+    participant_factory(
+        exchange=exchange, name="Withdrawn", withdrawn_at=datetime.now(UTC)
+    )
+
+    response = client.get(url_for("participant.dashboard", id=exchange.id))
+
+    assert response.status_code == 200
+    assert b"Active" in response.data
+    assert b"Withdrawn" not in response.data
+    # Count should be 2 (auth_participant + Active)
+    assert b"Participants (2)" in response.data
+
+
+def test_participant_list_shows_self_badge(client, auth_participant):
+    """Test participant list marks current user with badge."""
+    exchange = auth_participant.exchange
+
+    response = client.get(url_for("participant.dashboard", id=exchange.id))
+
+    assert response.status_code == 200
+    # Should show the participant's name
+    assert auth_participant.name.encode() in response.data
+    # Should show "You" badge
+    assert b"You" in response.data
+
+
+def test_participant_list_ordered_by_name(
+    client, auth_participant, participant_factory
+):
+    """Test participants are shown in alphabetical order."""
+    exchange = auth_participant.exchange
+
+    # Create participants with names that should be sorted
+    participant_factory(exchange=exchange, name="Zoe")
+    participant_factory(exchange=exchange, name="Alice")
+    participant_factory(exchange=exchange, name="Bob")
+
+    response = client.get(url_for("participant.dashboard", id=exchange.id))
+
+    assert response.status_code == 200
+    # Check order by finding positions in response
+    data = response.data.decode()
+    alice_pos = data.find("Alice")
+    bob_pos = data.find("Bob")
+    zoe_pos = data.find("Zoe")
+
+    # All should be present
+    assert alice_pos > 0
+    assert bob_pos > 0
+    assert zoe_pos > 0
+
+    # Should be in alphabetical order
+    assert alice_pos < bob_pos < zoe_pos
+
+
+def test_participant_list_empty_state(client, exchange_factory, participant_factory):
+    """Test message shown when only one participant."""
+    exchange = exchange_factory(state="registration_open")
+    participant = participant_factory(exchange=exchange)
+
+    # Create session for the only participant
+    with client.session_transaction() as session:
+        session["user_id"] = participant.id
+        session["user_type"] = "participant"
+        session["exchange_id"] = exchange.id
+
+    response = client.get(url_for("participant.dashboard", id=exchange.id))
+
+    assert response.status_code == 200
+    assert b"Participants (1)" in response.data
+    # Should show participant's own name
+    assert participant.name.encode() in response.data
+
+
+def test_participant_list_requires_auth(client, exchange_factory):
+    """Test participant list requires authentication."""
+    exchange = exchange_factory()
+
+    response = client.get(
+        url_for("participant.dashboard", id=exchange.id), follow_redirects=False
+    )
+
+    # Should redirect to login (or show error)
+    assert response.status_code in [302, 403]
+
+
+def test_participant_list_different_exchange(
+    client, auth_participant, exchange_factory, participant_factory
+):
+    """Test participants filtered by exchange."""
+    exchange1 = auth_participant.exchange
+    exchange2 = exchange_factory(state="registration_open")
+
+    # Create participant in different exchange
+    participant_factory(exchange=exchange2, name="Other Exchange")
+
+    response = client.get(url_for("participant.dashboard", id=exchange1.id))
+
+    assert response.status_code == 200
+    # Should not show participant from other exchange
+    assert b"Other Exchange" not in response.data