Feature/delta team/epic r04 (#7)

## Summary

epic r04 - begin refactor

## Change Type

- [x] Cowork feature
- [ ] Bug fix
- [ ] Core AI contribution
- [ ] Test / hardening
- [ ] Performance
- [ ] Documentation

## Related Work

Cowork Task:

Core Repo: http://34.143.229.138/gitea-admin/fsg-ai-core-assets

Core AI Issue:

Core Task:

Related PR:

## Scope

What is intentionally included?

What is intentionally NOT included?

## Validation

- [ ] Unit tests
- [ ] Integration tests
- [ ] Manual verification
- [ ] Regression check

Commands / evidence:

## Security Impact

Permission / credential / network / customer data impact:

## Compatibility

- [ ] No breaking change
- [ ] Breaking change documented

## Reviewer Notes

Anything Cowork reviewers should pay attention to.

---------

Co-authored-by: Anh Tran Nguyen Minh <anhtnm1@fpt.com>
Co-authored-by: Huong Le Thi Thien <huongltt35@fpt.com>
Co-authored-by: Nam Pham Dinh Thanh <nampdt@fpt.com>
Co-authored-by: Vu Dam Tuan <vudt15@fpt.com>
Co-authored-by: Hiep Ha Van <hiephv3@fpt.com>
Co-authored-by: Lam Hoang Van <lamhv7@fpt.com>
Reviewed-on: #7
Co-authored-by: Duy Le Huu <duylh19@fpt.com>

core/custom_icons.py

@@ -18,15 +18,18 @@ _MAX_BYTES = 200_000
 
 
 def icons_dir() -> Path:
+    """Thư mục chứa icon do người dùng thêm."""
     return ICONS_DIR
 
 
 def slugify(name: str) -> str:
+    """Định danh an toàn cho tên file icon; rỗng thì trả về 'icon'."""
     s = "".join(c if (c.isalnum() or c in "-_") else "-" for c in (name or "").strip().lower())
     return "-".join(filter(None, s.split("-"))) or "icon"
 
 
 def list_custom(directory: Optional[Path] = None) -> List[str]:
+    """Tên các icon tự thêm; thư mục chưa có thì trả list rỗng."""
     directory = directory or ICONS_DIR
     if not directory.exists():
         return []
@@ -69,6 +72,7 @@ def add_from_file(path, name: str = "", directory: Optional[Path] = None) -> str
 
 
 def delete_custom(name: str, directory: Optional[Path] = None) -> None:
+    """Xoá một icon tự thêm; không có thì bỏ qua."""
     directory = directory or ICONS_DIR
     path = directory / f"{slugify(name)}.svg"
     if path.exists():