v0.3.0 -- privacyfox-apply --revert

Adds privacyfox-apply --revert, closing a real gap found by actually testing a full uninstall: sudo apt purge privacyfox correctly undoes the system-wide side (policies.json, force-installed extensions), but was never able to touch the profile's user.js/userContent.css since those live in $HOME, same restriction that keeps the initial apply step out of postinst in the first place.

--revert restores the newest pre-PrivacyFox backup of user.js and userContent.css (made automatically on every apply run), or removes the file outright if no backup exists -- i.e. that profile had neither file before PrivacyFox touched it.

Correct full-uninstall order:

privacyfox-apply --revert
sudo apt purge privacyfox

Run --revert first -- purge removes the privacyfox-apply command itself along with the rest of the package.

Also fixes: apply now backs up userContent.css before overwriting it too (previously only user.js was backed up), and the man page's SEE ALSO section, which still named the old distribution/policies.json path from before 0.2.1's conffile-collision fix.

Tested against a fake profile before trusting it: real apply/backup/revert cycle, plus the no-backup case (profile that never had either file). Rebuilt, lintian-clean.