v4.0.0: behind-subject occlusion, a schema that says what it means, and only-live controls

- Fix "Behind Subject" not occluding: blur the two halves separately and
  re-apply the silhouette after, add a traced cast shadow (shadow_strength,
  shadow_length), and give the background glow real radial falloff
- Replace use_colored_lights with lighting_mode, adding "Both"; three presets
  set a colour and a grading block, so 12 values in each were inert
- Rename use_gradient_mode to mask_shape, and collapse apply_3d_lighting plus
  light_direction into subject_interaction
- Remove show_debug_info: wiring debug_image is the whole gesture, tracked
  through a hidden debug_output_connected input so one run is enough
- Scale everything drawn on the debug view with the frame, and flip a light's
  label to the left of the marker when it would run off the right edge
- Show only the controls that are doing something; grey out what a preset
  owns and put the preset's value in the label
- Ship a working "Fix node (recreate)" and remove ComfyUI-Manager's broken one
- Remap pre-v4 saves by name in web/relight_migrate.js
- Make "Rim Light (Behind)" a neutral white rim instead of (200,255,200)
- Drop requirements.txt; numpy, Pillow, scipy and torch come with ComfyUI
- Add a frontend test suite driving the real web/*.js outside a browser, and
  a CI job for it
- Bump to 4.0.0

example_workflows/relight_basic.json

@@ -215,7 +215,7 @@
       ],
       "size": [
         317.4000244140625,
-        1226
+        1250
       ],
       "flags": {},
       "order": 3,
@@ -260,17 +260,18 @@
       },
       "widgets_values": [
         "Warm Sunset Glow",
+        true,
+        "Color Correction",
+        "Radial falloff",
+        "Light behind subject (rim)",
+        true,
         1,
-        true,
-        true,
-        false,
-        false,
-        true,
-        "Behind Subject",
-        true,
         1,
         50,
         2,
+        0.6,
+        0.35,
+        true,
         0.26000000000000006,
         0.31000000000000005,
         0.4,
@@ -380,4 +381,4 @@
     }
   },
   "version": 0.4
-}
+}