Remove redundant configs/birefnet.yaml; drop a stray --config example

BiRefNet is the default backend and --seg-backend switches segmenters, so the
birefnet.yaml config (a copy of default.yaml with backend: birefnet) no longer had
a purpose. configs/ now holds just default.yaml, the editable parameter template.
Also dropped the now-redundant --config from the chroma-debug README example.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -103,7 +103,6 @@ D:\MiniConda\envs\lightML\python.exe -m bgfilter.cli `
   --input-dir Samples `
   --output-dir Outputs\chroma `
   --debug-dir Outputs\chroma_debug `
-  --config configs\default.yaml `
   --matting-method chroma `
   --device cpu
 ```

configs/birefnet.yaml

@@ -1,60 +0,0 @@
-# Same as default.yaml but with the BiRefNet segmentation backend instead of
-# anime-seg. BiRefNet is a general salient-object segmenter (not anime-specific),
-# so it can find subjects anime-seg misses. It ships custom modelling code, so it
-# needs trust_remote_code (handled in code) plus timm / einops / kornia, and the
-# first run downloads weights from HuggingFace (set HF_ENDPOINT behind a firewall).
-screen_color: null
-
-model:
-  model_name: hustvl/vitmatte-base-composition-1k
-  device: cpu
-  matting_method: vitmatte
-  fallback_to_chroma_alpha: false
-
-segmentation:
-  enabled: true
-  backend: birefnet
-  model_name: ZhengPeng7/BiRefNet
-  device: cpu
-  input_size: 1024
-
-trimap:
-  sure_bg_threshold: 0.92
-  sure_fg_threshold: 0.12
-  unknown_radius_ratio: 0.012
-  fg_safe_radius_ratio: 0.006
-  seg_core_threshold: 0.60
-  seg_loose_threshold: 0.08
-  mode: directional
-  seg_low: 0.15
-  bg_hue_proj_min: 4.0
-
-alpha_post:
-  chroma_suppress: true
-  chroma_suppress_bg_low: 0.35
-  chroma_suppress_bg_high: 0.80
-  chroma_suppress_strength: 1.0
-
-foreground:
-  enabled: true
-  method: ml
-  fallback_to_unmix: true
-  ml_regularization: 0.00001
-  edge_low: 0.005
-  edge_high: 0.995
-  min_unmix_alpha: 0.08
-  unmix_strength: 0.70
-  local_strength: 0.45
-  local_blur_radius: 11
-  local_alpha_threshold: 0.92
-  local_bg_confidence_max: 0.20
-  green_excess_margin: 0.015
-  bg_confidence_weight: 0.70
-
-despill:
-  enabled: true
-  edge_low: 0.005
-  strength: 0.92
-  edge_expand_radius: 2
-  alpha_weight_floor: 0.35
-  color_margin_lab: 4.0