chore: prepare repo for public release

Remove hardcoded personal session cookie from run.py, translate all
text to English, fix a missing-newline bug in the link generator,
auto-create working directories, and add a GPLv3 license.

.gitignore

@@ -0,0 +1,11 @@
+__pycache__/
+*.py[cod]
+.venv/
+venv/
+*.log
+
+# Runtime data, not meant to be versioned
+links.txt
+downloading/
+finished/
+.env