Move release scripts to private .scripts folder

- Remove release-agent.py, build-nightly.py from public repo
- Add .scripts/ to .gitignore for private tools
- Maintain clean public repository while keeping internal tools

.gitignore

@@ -1,3 +1,6 @@
+# Scripts folder (private tools)
+.scripts/
+
 # Byte-compiled / optimized / DLL files
 __pycache__/
 *.py[cod]