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/gen_plate_pool.py

@@ -49,6 +49,8 @@ from plate_number import (
 
 # 类型配置
 PLATE_TYPES = [
+    ('blue',        'blue',        generate_plate_number_blue),
+    ('green',       'green_car',   lambda: generate_plate_number_blue(length=8)),
     ('police',      'white',       generate_plate_number_white),
     ('army',        'white_army',  generate_plate_number_army),
     ('gangao',      'black',       generate_plate_number_black_gangao),