add resume support, metadata paths, LRCLIB order and overall progress

- store source track path in metadata.json and validate it when skipping ready files
- add skip_existing/resume_partial options to config and GUI
- identify lyrics via embedded text, Shazam, then one LRCLIB author search
- keep post-ASR LRCLIB text matching and allow cancelling safely
- recover from CUDA OOM and free VRAM between batch stages
- add overall completed/total file progress bar to GUI and pipelines

core/config.py

@@ -81,6 +81,9 @@ class PipelineConfig:
     keep_intermediate: bool = True
     overwrite: bool = True
     mode: str = "sequential"
+    chunk_size: int = 64
+    skip_existing: bool = False     # skip files that already have text.txt
+    resume_partial: bool = True     # reuse existing vocals.wav / convert.wav
 
     convert: ConvertConfig = field(default_factory=ConvertConfig)
     separate: SeparateConfig = field(default_factory=SeparateConfig)