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/unit/test_participant_utils.py

@@ -0,0 +1,123 @@
+"""Unit tests for participant utility functions."""
+
+from datetime import UTC, datetime
+
+from src.utils.participant import (
+    can_update_profile,
+    get_active_participants,
+    is_withdrawn,
+)
+
+
+def test_get_active_participants_excludes_withdrawn(
+    exchange_factory, participant_factory
+):
+    """Test that get_active_participants excludes withdrawn participants."""
+    exchange = exchange_factory()
+
+    # Create 2 active, 1 withdrawn
+    active1 = participant_factory(exchange=exchange, name="Alice")
+    active2 = participant_factory(exchange=exchange, name="Bob")
+    withdrawn = participant_factory(
+        exchange=exchange, name="Charlie", withdrawn_at=datetime.now(UTC)
+    )
+
+    participants = get_active_participants(exchange.id)
+
+    assert len(participants) == 2
+    assert active1 in participants
+    assert active2 in participants
+    assert withdrawn not in participants
+
+
+def test_get_active_participants_ordered_by_name(exchange_factory, participant_factory):
+    """Test that participants are ordered alphabetically."""
+    exchange = exchange_factory()
+
+    participant_factory(exchange=exchange, name="Zoe")
+    participant_factory(exchange=exchange, name="Alice")
+    participant_factory(exchange=exchange, name="Bob")
+
+    participants = get_active_participants(exchange.id)
+
+    assert len(participants) == 3
+    assert participants[0].name == "Alice"
+    assert participants[1].name == "Bob"
+    assert participants[2].name == "Zoe"
+
+
+def test_get_active_participants_empty_when_all_withdrawn(
+    exchange_factory, participant_factory
+):
+    """Test that empty list returned when all participants withdrawn."""
+    exchange = exchange_factory()
+
+    participant_factory(exchange=exchange, withdrawn_at=datetime.now(UTC))
+    participant_factory(exchange=exchange, withdrawn_at=datetime.now(UTC))
+
+    participants = get_active_participants(exchange.id)
+
+    assert len(participants) == 0
+
+
+def test_get_active_participants_different_exchanges(
+    exchange_factory, participant_factory
+):
+    """Test that participants are filtered by exchange_id."""
+    exchange1 = exchange_factory()
+    exchange2 = exchange_factory()
+
+    participant_factory(exchange=exchange1, name="Alice")
+    participant_factory(exchange=exchange2, name="Bob")
+
+    participants = get_active_participants(exchange1.id)
+
+    assert len(participants) == 1
+    assert participants[0].name == "Alice"
+
+
+def test_is_withdrawn_true(participant_factory):
+    """Test is_withdrawn returns True for withdrawn participant."""
+    participant = participant_factory(withdrawn_at=datetime.now(UTC))
+    assert is_withdrawn(participant) is True
+
+
+def test_is_withdrawn_false(participant_factory):
+    """Test is_withdrawn returns False for active participant."""
+    participant = participant_factory()
+    assert is_withdrawn(participant) is False
+
+
+def test_can_update_profile_draft_state(participant_factory, exchange_factory):
+    """Profile updates allowed in draft state."""
+    exchange = exchange_factory(state="draft")
+    participant = participant_factory(exchange=exchange)
+    assert can_update_profile(participant) is True
+
+
+def test_can_update_profile_registration_open(participant_factory, exchange_factory):
+    """Profile updates allowed when registration open."""
+    exchange = exchange_factory(state="registration_open")
+    participant = participant_factory(exchange=exchange)
+    assert can_update_profile(participant) is True
+
+
+def test_can_update_profile_registration_closed(participant_factory, exchange_factory):
+    """Profile updates allowed when registration closed."""
+    exchange = exchange_factory(state="registration_closed")
+    participant = participant_factory(exchange=exchange)
+    assert can_update_profile(participant) is True
+
+
+def test_can_update_profile_matched_state(participant_factory, exchange_factory):
+    """Profile updates blocked after matching."""
+    exchange = exchange_factory(state="matched")
+    participant = participant_factory(exchange=exchange)
+    assert can_update_profile(participant) is False
+
+
+def test_can_update_profile_completed_state(participant_factory, exchange_factory):
+    """Profile updates blocked when completed."""
+    exchange = exchange_factory(state="completed")
+    participant = participant_factory(exchange=exchange)
+    assert can_update_profile(participant) is False