test: run and fix V2 API tests - 11/18 passing

Changes:
- Fixed UserResponse schema datetime serialization bug
- Fixed test_auth.py mock structure for external auth service
- Updated conftest.py to create fresh database per test
- Ran full test suite and verified results

Test Results:
✅ test_auth.py: 5/5 passing (100%)
✅ test_tasks.py: 4/6 passing (67%)
✅ test_admin.py: 2/4 passing (50%)
❌ test_integration.py: 0/3 passing (0%)

Total: 11/18 tests passing (61%)

Known Issues:
1. Fixture isolation: test_user sometimes gets admin email
2. Admin API response structure doesn't match test expectations
3. Integration tests need mock fixes

Production Bug Fixed:
- UserResponse schema now properly serializes datetime fields to ISO format strings

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

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

backend/tests/conftest_v1.py

@@ -0,0 +1,179 @@
+"""
+Tool_OCR - Pytest Fixtures and Configuration
+Shared fixtures for all tests
+"""
+
+import pytest
+import tempfile
+import shutil
+from pathlib import Path
+from PIL import Image
+import io
+
+from app.services.preprocessor import DocumentPreprocessor
+
+
+@pytest.fixture
+def temp_dir():
+    """Create a temporary directory for test files"""
+    temp_path = Path(tempfile.mkdtemp())
+    yield temp_path
+    # Cleanup after test
+    shutil.rmtree(temp_path, ignore_errors=True)
+
+
+@pytest.fixture
+def sample_image_path(temp_dir):
+    """Create a valid PNG image file for testing"""
+    image_path = temp_dir / "test_image.png"
+
+    # Create a simple 100x100 white image
+    img = Image.new('RGB', (100, 100), color='white')
+    img.save(image_path, 'PNG')
+
+    return image_path
+
+
+@pytest.fixture
+def sample_jpg_path(temp_dir):
+    """Create a valid JPG image file for testing"""
+    image_path = temp_dir / "test_image.jpg"
+
+    # Create a simple 100x100 white image
+    img = Image.new('RGB', (100, 100), color='white')
+    img.save(image_path, 'JPEG')
+
+    return image_path
+
+
+@pytest.fixture
+def sample_pdf_path(temp_dir):
+    """Create a valid PDF file for testing"""
+    pdf_path = temp_dir / "test_document.pdf"
+
+    # Create minimal valid PDF
+    pdf_content = b"""%PDF-1.4
+1 0 obj
+<<
+/Type /Catalog
+/Pages 2 0 R
+>>
+endobj
+2 0 obj
+<<
+/Type /Pages
+/Kids [3 0 R]
+/Count 1
+>>
+endobj
+3 0 obj
+<<
+/Type /Page
+/Parent 2 0 R
+/MediaBox [0 0 612 792]
+/Contents 4 0 R
+/Resources <<
+/Font <<
+/F1 <<
+/Type /Font
+/Subtype /Type1
+/BaseFont /Helvetica
+>>
+>>
+>>
+>>
+endobj
+4 0 obj
+<<
+/Length 44
+>>
+stream
+BT
+/F1 12 Tf
+100 700 Td
+(Test PDF) Tj
+ET
+endstream
+endobj
+xref
+0 5
+0000000000 65535 f
+0000000009 00000 n
+0000000058 00000 n
+0000000115 00000 n
+0000000317 00000 n
+trailer
+<<
+/Size 5
+/Root 1 0 R
+>>
+startxref
+410
+%%EOF
+"""
+
+    with open(pdf_path, 'wb') as f:
+        f.write(pdf_content)
+
+    return pdf_path
+
+
+@pytest.fixture
+def corrupted_image_path(temp_dir):
+    """Create a corrupted image file for testing"""
+    image_path = temp_dir / "corrupted.png"
+
+    # Write invalid PNG data
+    with open(image_path, 'wb') as f:
+        f.write(b'\x89PNG\r\n\x1a\n\x00\x00\x00corrupted data')
+
+    return image_path
+
+
+@pytest.fixture
+def large_file_path(temp_dir):
+    """Create a valid PNG file larger than the upload limit"""
+    file_path = temp_dir / "large_file.png"
+
+    # Create a large PNG image with random data (to prevent compression)
+    # 15000x15000 with random pixels should be > 20MB
+    import numpy as np
+    random_data = np.random.randint(0, 256, (15000, 15000, 3), dtype=np.uint8)
+    img = Image.fromarray(random_data, 'RGB')
+    img.save(file_path, 'PNG', compress_level=0)  # No compression
+
+    # Verify it's actually large
+    file_size = file_path.stat().st_size
+    assert file_size > 20 * 1024 * 1024, f"File only {file_size / (1024*1024):.2f} MB"
+
+    return file_path
+
+
+@pytest.fixture
+def unsupported_file_path(temp_dir):
+    """Create a file with unsupported format"""
+    file_path = temp_dir / "test.txt"
+
+    with open(file_path, 'w') as f:
+        f.write("This is a text file, not an image")
+
+    return file_path
+
+
+@pytest.fixture
+def preprocessor():
+    """Create a DocumentPreprocessor instance"""
+    return DocumentPreprocessor()
+
+
+@pytest.fixture
+def sample_image_with_text():
+    """Return path to a real image with text from demo_docs for OCR testing"""
+    # Use the english.png sample from demo_docs
+    demo_image_path = Path(__file__).parent.parent.parent / "demo_docs" / "basic" / "english.png"
+
+    # Check if demo image exists, otherwise skip the test
+    if not demo_image_path.exists():
+        pytest.skip(f"Demo image not found at {demo_image_path}")
+
+    return demo_image_path