Dataset: add READMEs, organize scripts, update .gitignore

- Add README.md to all 16 dataset directories with script references
- Centralize generation scripts under scripts/ with full README
- Update .gitignore to cover all data directories, keep only metadata
- Remove redundant CCPD/.gitignore (parent covers same rules)
- Remove stale scripts/test/ (254MB pipeline residue)
- Fix label parser reference: scripts are authoritative source of truth

CCPD_SPE_GEN/cpp_pipeline/plate_swap.hpp

@@ -34,7 +34,6 @@ struct SwapConfig {
     std::string plate_type;
     std::string output_dir;
     int h_shift = 0, s_scale = 100, v_scale = 100;
-    bool fast_mode = false;
 };
 
 // 单张处理 (pre-parsed meta 避免重复解析)