feat: Implement dispute flow with status machine and audit trail

- Added full dispute status machine (open → evidence → mediation → resolved → cancelled)
- Implemented event logging for all dispute actions
- Added audit trail through dispute_events table
- Updated dispute service with proper status transition handling
- Ensured final decisions include reasoning for auditability

Fixes #5

test-dispute-flow.js

@@ -0,0 +1,103 @@
+const { DisputeService } = require('./backend/src/disputes/dispute-service');
+const { DB } = require('./backend/src/db');
+
+// Mock database for testing
+class MockDB {
+  constructor() {
+    this.queries = [];
+  }
+
+  async query(sql, params) {
+    this.queries.push({ sql, params });
+    
+    // Return mock results based on SQL
+    if (sql.includes('INSERT INTO disputes')) {
+      return { insertId: 1 };
+    }
+    if (sql.includes('SELECT * FROM disputes WHERE id = ?')) {
+      return [[{
+        id: 1,
+        deal_id: 123,
+        opened_by_user_id: 456,
+        status: 'open',
+        reason_code: 'NO_SHOW',
+        summary: 'Test dispute',
+        requested_outcome: 'refund',
+        created_at: '2026-03-19T14:00:00Z',
+        updated_at: '2026-03-19T14:00:00Z'
+      }]];
+    }
+    if (sql.includes('SELECT * FROM dispute_events WHERE dispute_id = ?')) {
+      return [[]];
+    }
+    return [];
+  }
+}
+
+// Test the dispute service
+async function testDisputeService() {
+  console.log('Testing Dispute Service...');
+  
+  const mockDB = new MockDB();
+  const disputeService = new DisputeService(mockDB);
+  
+  try {
+    // Test creating a dispute
+    console.log('1. Testing createDispute...');
+    const dispute = await disputeService.createDispute({
+      deal_id: 123,
+      opened_by_user_id: 456,
+      reason_code: 'NO_SHOW',
+      summary: 'Test dispute',
+      requested_outcome: 'refund'
+    });
+    
+    console.log('✓ Dispute created successfully');
+    console.log('Dispute ID:', dispute.id);
+    
+    // Test getting a dispute
+    console.log('2. Testing getDisputeById...');
+    const retrievedDispute = await disputeService.getDisputeById(1);
+    console.log('✓ Dispute retrieved successfully');
+    console.log('Status:', retrievedDispute.status);
+    
+    // Test updating status
+    console.log('3. Testing updateDisputeStatus...');
+    await disputeService.updateDisputeStatus(1, 'evidence', 456);
+    console.log('✓ Status updated successfully');
+    
+    // Test adding evidence
+    console.log('4. Testing addEvidence...');
+    await disputeService.addEvidence(1, 456, { file: 'test.jpg' });
+    console.log('✓ Evidence added successfully');
+    
+    // Test resolving dispute
+    console.log('5. Testing resolveDispute...');
+    await disputeService.resolveDispute(1, 456, 'refund', 'User did not show up');
+    console.log('✓ Dispute resolved successfully');
+    
+    // Test getting events
+    console.log('6. Testing getDisputeEvents...');
+    const events = await disputeService.getDisputeEvents(1);
+    console.log('✓ Events retrieved successfully');
+    console.log('Number of events:', events.length);
+    
+    console.log('\n🎉 All tests passed!');
+    
+  } catch (error) {
+    console.error('❌ Test failed:', error.message);
+    return false;
+  }
+  
+  return true;
+}
+
+// Run the test
+testDisputeService().then(success => {
+  if (success) {
+    console.log('\n✅ All tests completed successfully');
+  } else {
+    console.log('\n❌ Some tests failed');
+    process.exit(1);
+  }
+});