Migrate database from SQLite to PostgreSQL

- Replace SQLite with PostgreSQL using Neon as provider
- Add environment-based database URL configuration
- Create separate test database setup with DATABASE_URL_TEST
- Reset migration history and generate fresh PostgreSQL schema
- Add comprehensive migration documentation
- Include database unit tests for connection validation

tests/unit/database.test.ts

@@ -0,0 +1,77 @@
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import { PrismaClient } from '@prisma/client';
+
+describe('Database Configuration', () => {
+  let prisma: PrismaClient;
+
+  beforeAll(() => {
+    prisma = new PrismaClient();
+  });
+
+  afterAll(async () => {
+    await prisma.$disconnect();
+  });
+
+  it('should connect to the test database', async () => {
+    // Verify we can connect to the database
+    const result = await prisma.$queryRaw`SELECT 1 as test`;
+    expect(result).toBeDefined();
+  });
+
+  it('should use PostgreSQL as the database provider', async () => {
+    // Query the database to verify it's PostgreSQL
+    const result = await prisma.$queryRaw`SELECT version()` as any[];
+    expect(result[0].version).toContain('PostgreSQL');
+  });
+
+  it('should be using the test database URL', () => {
+    // Verify that DATABASE_URL is set to the test database
+    expect(process.env.DATABASE_URL).toBeDefined();
+    expect(process.env.DATABASE_URL).toContain('postgresql://');
+    
+    // If DATABASE_URL_TEST is set, DATABASE_URL should match it (from our test setup)
+    if (process.env.DATABASE_URL_TEST) {
+      expect(process.env.DATABASE_URL).toBe(process.env.DATABASE_URL_TEST);
+    }
+  });
+
+  it('should have all required tables', async () => {
+    // Verify all our tables exist
+    const tables = await prisma.$queryRaw`
+      SELECT table_name 
+      FROM information_schema.tables 
+      WHERE table_schema = 'public' 
+      AND table_type = 'BASE TABLE'
+      ORDER BY table_name
+    ` as any[];
+
+    const tableNames = tables.map(t => t.table_name);
+    
+    expect(tableNames).toContain('Company');
+    expect(tableNames).toContain('User');
+    expect(tableNames).toContain('Session');
+    expect(tableNames).toContain('SessionImport');
+    expect(tableNames).toContain('Message');
+    expect(tableNames).toContain('Question');
+    expect(tableNames).toContain('SessionQuestion');
+    expect(tableNames).toContain('AIProcessingRequest');
+  });
+
+  it('should be able to create and query data', async () => {
+    // Test basic CRUD operations
+    const company = await prisma.company.create({
+      data: {
+        name: 'Test Company',
+        csvUrl: 'https://example.com/test.csv',
+      },
+    });
+
+    expect(company.id).toBeDefined();
+    expect(company.name).toBe('Test Company');
+
+    // Clean up
+    await prisma.company.delete({
+      where: { id: company.id },
+    });
+  });
+});