Lint cleanup: ruff fixes across entire codebase

- Strip trailing whitespace from all Python files
- Fix import sorting (I001) across all modules
- Convert Optional[X] to X | None syntax (UP045)
- Remove unused imports (F401)
- Convert lambda assignments to def functions (E731)
- Add TYPE_CHECKING import for forward references
- Update pyproject.toml ruff config:
  - Move select/ignore to [tool.ruff.lint] section
  - Add per-file ignores for DCT colorspace naming (N803/N806)
  - Add per-file ignores for __init__.py import structure (E402)
  - Exclude defunct test_routes.py
- Remove frontends/web/test_routes.py (defunct debug snippet)

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

check_scipy.py

@@ -51,30 +51,30 @@ print("Testing scipy DCT...")
 try:
     from scipy.fftpack import dct, idct
     import numpy as np
-    
+
     # Create test array
     test = np.random.rand(8, 8).astype(np.float64)
     print(f"Input array shape: {test.shape}, dtype: {test.dtype}")
-    
+
     # Test 1D DCT
     row = test[0, :]
     result = dct(row, norm='ortho')
     print(f"1D DCT result shape: {result.shape}, dtype: {result.dtype}")
-    
+
     # Test 2D DCT (the potentially problematic operation)
     result2d = dct(dct(test.T, norm='ortho').T, norm='ortho')
     print(f"2D DCT result shape: {result2d.shape}, dtype: {result2d.dtype}")
-    
+
     # Test inverse
     recovered = idct(idct(result2d.T, norm='ortho').T, norm='ortho')
     error = np.max(np.abs(test - recovered))
     print(f"Round-trip error: {error}")
-    
+
     if error < 1e-10:
         print("✓ scipy DCT working correctly")
     else:
         print("⚠ scipy DCT has precision issues")
-        
+
 except Exception as e:
     print(f"✗ scipy DCT failed: {e}")
     import traceback
@@ -90,11 +90,11 @@ try:
     from scipy.fftpack import dct, idct
     import numpy as np
     import gc
-    
+
     # Simulate processing many 8x8 blocks
     large_array = np.random.rand(512, 512).astype(np.float64)
     print(f"Large array shape: {large_array.shape}, size: {large_array.nbytes} bytes")
-    
+
     count = 0
     for y in range(0, 512, 8):
         for x in range(0, 512, 8):
@@ -103,14 +103,14 @@ try:
             recovered = idct(idct(dct_block.T, norm='ortho').T, norm='ortho')
             large_array[y:y+8, x:x+8] = recovered
             count += 1
-    
+
     print(f"Processed {count} blocks successfully")
-    
+
     del large_array
     gc.collect()
-    
+
     print("✓ Large array processing completed")
-    
+
 except Exception as e:
     print(f"✗ Large array processing failed: {e}")
     import traceback
@@ -125,26 +125,26 @@ print("Testing PIL with large image...")
 try:
     from PIL import Image
     import io
-    
+
     # Create a large test image
     img = Image.new('RGB', (4000, 3000), color=(128, 128, 128))
-    
+
     # Save to bytes
     buffer = io.BytesIO()
     img.save(buffer, format='PNG')
     img_bytes = buffer.getvalue()
     print(f"Test image size: {len(img_bytes)} bytes")
-    
+
     # Re-open and process
     buffer2 = io.BytesIO(img_bytes)
     img2 = Image.open(buffer2)
     print(f"Re-opened image: {img2.size}, mode: {img2.mode}")
-    
+
     # Convert to numpy array
     import numpy as np
     arr = np.array(img2)
     print(f"NumPy array: {arr.shape}, dtype: {arr.dtype}")
-    
+
     # Clean up
     img.close()
     img2.close()
@@ -152,9 +152,9 @@ try:
     buffer2.close()
     del arr
     gc.collect()
-    
+
     print("✓ PIL large image test completed")
-    
+
 except Exception as e:
     print(f"✗ PIL test failed: {e}")
     import traceback