Initial commit: doujinshi-dl generic plugin framework

History reset as part of DMCA compliance. The project has been
refactored into a generic, site-agnostic download framework.
Site-specific logic lives in separate plugin packages.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

doujinshi_dl/constant.py

@@ -0,0 +1,9 @@
+# coding: utf-8
+"""Main-package constants.
+
+Only the constants that the main package itself needs are defined here.
+Plugin-specific constants live in the respective plugin package.
+"""
+import os
+
+PATH_SEPARATOR = os.path.sep