license: Clean up Apache 2.0 transition (fixes #1235)

- Remove LICENSE.txt (old LGPL 2.1 file)
- Update pyproject.toml to reference LICENSE and use Apache classifier
- Update __init__.py docstring with Apache 2.0 notice
- Standardize copyright: 2014-2026 DataJoint Inc. and contributors

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: dimitri-yatsenko

LICENSE

@@ -175,7 +175,7 @@
 
    END OF TERMS AND CONDITIONS
 
-   Copyright 2024 DataJoint Inc. and contributors
+   Copyright 2014-2026 DataJoint Inc. and contributors
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.