test: Phase 2 - Create test infrastructure

- Create comprehensive test directory structure
- Implement better-sqlite3 mock for Vitest
- Add node factory using fishery for test data generation
- Create workflow builder with fluent API
- Add infrastructure validation tests
- Update testing checklist to reflect progress

All Phase 2 tasks completed successfully with 7 tests passing.

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

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

tests/unit/database/__mocks__/better-sqlite3.ts

@@ -0,0 +1,53 @@
+import { vi } from 'vitest';
+
+export class MockDatabase {
+  private data = new Map<string, any[]>();
+  private prepared = new Map<string, any>();
+  
+  constructor() {
+    this.data.set('nodes', []);
+    this.data.set('templates', []);
+    this.data.set('tools_documentation', []);
+  }
+  
+  prepare(sql: string) {
+    const key = this.extractTableName(sql);
+    
+    return {
+      all: vi.fn(() => this.data.get(key) || []),
+      get: vi.fn((id: string) => {
+        const items = this.data.get(key) || [];
+        return items.find(item => item.id === id);
+      }),
+      run: vi.fn((params: any) => {
+        const items = this.data.get(key) || [];
+        items.push(params);
+        this.data.set(key, items);
+        return { changes: 1, lastInsertRowid: items.length };
+      })
+    };
+  }
+  
+  exec(sql: string) {
+    // Mock schema creation
+    return true;
+  }
+  
+  close() {
+    // Mock close
+    return true;
+  }
+  
+  // Helper to extract table name from SQL
+  private extractTableName(sql: string): string {
+    const match = sql.match(/FROM\s+(\w+)|INTO\s+(\w+)|UPDATE\s+(\w+)/i);
+    return match ? (match[1] || match[2] || match[3]) : 'nodes';
+  }
+  
+  // Test helper to seed data
+  _seedData(table: string, data: any[]) {
+    this.data.set(table, data);
+  }
+}
+
+export default vi.fn(() => new MockDatabase());