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>

test_dct_crash.py

@@ -61,16 +61,16 @@ except ImportError:
 print("\n[3] BASIC DCT TEST (8x8 block)")
 try:
     test_block = np.random.rand(8, 8).astype(np.float64)
-    
+
     # 1D DCT on rows
     result = dct(test_block[0, :], norm='ortho')
     print(f"  1D DCT: OK (output shape: {result.shape})")
-    
+
     # 1D IDCT
     recovered = idct(result, norm='ortho')
     error = np.max(np.abs(test_block[0, :] - recovered))
     print(f"  1D IDCT: OK (roundtrip error: {error:.2e})")
-    
+
     # 2D via separable
     temp = np.zeros_like(test_block)
     for i in range(8):
@@ -79,10 +79,10 @@ try:
     for i in range(8):
         result2d[i, :] = dct(temp[i, :], norm='ortho')
     print(f"  2D DCT: OK")
-    
+
     gc.collect()
     print("  GC after basic test: OK")
-    
+
 except Exception as e:
     print(f"  FAILED: {e}")
     traceback.print_exc()
@@ -92,10 +92,10 @@ print("\n[4] STRESS TEST (many 8x8 blocks)")
 try:
     NUM_BLOCKS = 10000
     print(f"  Processing {NUM_BLOCKS} blocks...")
-    
+
     for i in range(NUM_BLOCKS):
         block = np.random.rand(8, 8).astype(np.float64)
-        
+
         # Forward DCT
         temp = np.zeros_like(block)
         for j in range(8):
@@ -103,7 +103,7 @@ try:
         result = np.zeros_like(temp)
         for j in range(8):
             result[j, :] = dct(temp[j, :], norm='ortho')
-        
+
         # Inverse DCT
         temp2 = np.zeros_like(result)
         for j in range(8):
@@ -111,14 +111,14 @@ try:
         recovered = np.zeros_like(temp2)
         for j in range(8):
             recovered[:, j] = idct(temp2[:, j], norm='ortho')
-        
+
         if i % 1000 == 0:
             gc.collect()
             print(f"    {i}/{NUM_BLOCKS} blocks processed...")
-    
+
     gc.collect()
     print(f"  Stress test PASSED")
-    
+
 except Exception as e:
     print(f"  FAILED at block {i}: {e}")
     traceback.print_exc()
@@ -127,18 +127,18 @@ except Exception as e:
 if len(sys.argv) > 1:
     image_path = sys.argv[1]
     print(f"\n[5] IMAGE TEST: {image_path}")
-    
+
     try:
         with open(image_path, 'rb') as f:
             image_data = f.read()
         print(f"  File size: {len(image_data) / 1024 / 1024:.2f} MB")
-        
+
         img = Image.open(io.BytesIO(image_data))
         width, height = img.size
         print(f"  Dimensions: {width}x{height}")
         print(f"  Format: {img.format}")
         print(f"  Mode: {img.mode}")
-        
+
         # Convert to grayscale float array
         gray = img.convert('L')
         arr = np.array(gray, dtype=np.float64)
@@ -146,35 +146,35 @@ if len(sys.argv) > 1:
         gray.close()
         print(f"  Array shape: {arr.shape}")
         print(f"  Array dtype: {arr.dtype}")
-        
+
         # Pad to block boundary
         BLOCK_SIZE = 8
         h, w = arr.shape
         new_h = ((h + BLOCK_SIZE - 1) // BLOCK_SIZE) * BLOCK_SIZE
         new_w = ((w + BLOCK_SIZE - 1) // BLOCK_SIZE) * BLOCK_SIZE
-        
+
         if new_h != h or new_w != w:
             padded = np.zeros((new_h, new_w), dtype=np.float64)
             padded[:h, :w] = arr
             arr = padded
             print(f"  Padded to: {arr.shape}")
-        
+
         blocks_y = arr.shape[0] // BLOCK_SIZE
         blocks_x = arr.shape[1] // BLOCK_SIZE
         total_blocks = blocks_y * blocks_x
         print(f"  Total 8x8 blocks: {total_blocks}")
-        
+
         # Process ALL blocks
         print(f"  Processing all blocks with DCT...")
-        
+
         processed = 0
         for by in range(blocks_y):
             for bx in range(blocks_x):
                 y = by * BLOCK_SIZE
                 x = bx * BLOCK_SIZE
-                
+
                 block = arr[y:y+BLOCK_SIZE, x:x+BLOCK_SIZE].copy()
-                
+
                 # Forward DCT
                 temp = np.zeros((8, 8), dtype=np.float64)
                 for i in range(8):
@@ -182,7 +182,7 @@ if len(sys.argv) > 1:
                 dct_block = np.zeros((8, 8), dtype=np.float64)
                 for i in range(8):
                     dct_block[i, :] = dct(temp[i, :], norm='ortho')
-                
+
                 # Inverse DCT
                 temp2 = np.zeros((8, 8), dtype=np.float64)
                 for i in range(8):
@@ -190,17 +190,17 @@ if len(sys.argv) > 1:
                 recovered = np.zeros((8, 8), dtype=np.float64)
                 for i in range(8):
                     recovered[:, i] = idct(temp2[:, i], norm='ortho')
-                
+
                 processed += 1
-                
+
             # GC after each row of blocks
             if by % 50 == 0:
                 gc.collect()
                 print(f"    Row {by}/{blocks_y} ({processed}/{total_blocks} blocks)")
-        
+
         gc.collect()
         print(f"  Image DCT test PASSED ({processed} blocks)")
-        
+
     except Exception as e:
         print(f"  FAILED: {e}")
         traceback.print_exc()