Let's only keep instructions for stuff that we've seen the AI
mess up in practice rather than having a bunch of AI generated
text that it can figure out for itself these days (given it was
trained on systemd's source code in the first place).
Also add a rule to use git worktrees and check out PRs locally when
reviewing them, since I've seen it mess that up in practice.
This seems to be what all the tools are standardizing on, except
claude (https://github.com/anthropics/claude-code/issues/6235) so
add a symlink from CLAUDE.md to AGENTS.md for now until they support
it as well.
I also had claude extend the instructions a bit.
Co-developed-by: Claude <claude@anthropic.com>
