Overhaul contribution guide & add a AI policy (#6038)

* Overhaul contribution guide & add a AI policy

* Fix broken links

doc/development/contribution/ai.rst

@@ -0,0 +1,24 @@
+.. _`aipolicy`:
+
+AI-assisted contribution policy
+===============================
+
+pretix is maintained by humans.
+Every discussion, issue, and pull request is read and reviewed by humans (and sometimes machines, too).
+We ask you to respect the time and effort put in by these humans by not sending low-effort, unqualified work, since it puts the burden of validation on the maintainer.
+
+Therefore, the pretix project has strict rules for AI usage:
+
+- **All AI usage in any form must be disclosed.** You must state the tool you used (e.g. Claude Code, Cursor, Amp) along with the extent that the work was AI-assisted.
+
+- **The human-in-the-loop must fully understand all code.** If you can't explain what your changes do and how they interact with the greater system without the aid of AI tools, do not contribute to this project.
+
+- **Issues and discussions can use AI assistance but must have a full human-in-the-loop.** This means that any content generated with AI must have been reviewed and edited by a human before submission. AI is very good at being overly verbose and including noise that distracts from the main point. Humans must do their research and trim this down.
+
+- **No AI-generated media is allowed (art, images, videos, audio, etc.).** Text and code are the only acceptable AI-generated content, per the other rules in this policy.
+
+- **Bad AI drivers will be excluded from the project.** People who produce bad contributions that are clearly AI (slop) will be blocked from our organization without warning.
+
+This policy was inspired by the `ghostty project`_.
+
+.. _ghostty project: https://github.com/ghostty-org/ghostty/blob/main/AI_POLICY.md