docs: rewrite contributing guide, add QA and compatibility docs

Issues are bug-only now. The feature-request template is gone, requests
opened as issues get closed automatically, and feature talk moves to
product discussions on GitHub Discussions and Discord. "Product
discussion" is the term everywhere, recorded in the glossary.

Contributing states the QA evidence bar and links out instead of
teaching; docs/qa.md carries the depth. The protocol back-compat rules
moved out of CLAUDE.md into docs/protocol-compatibility.md, since that
constraint is invisible in development where both sides always run the
same version.

CLAUDE.md gains doc-writing and voice rules to keep docs from
accumulating appended paragraphs. design.md gains an alignment section
(glyph rails) and a layout-shift rule.

.github/ISSUE_TEMPLATE/config.yml

@@ -1,5 +1,8 @@
 blank_issues_enabled: false
 contact_links:
-  - name: Discord
+  - name: Product discussion on Discord
     url: https://discord.gg/jz8T2uahpH
-    about: Urgent or blocking issues, quick questions, sharing a video of a bug, or anything that's better as a chat.
+    about: Any discussion, product or otherwise. Product discussions go in #product — describe what you're trying to do, how you do it today, and where Paseo gets in the way.
+  - name: Product discussion on GitHub
+    url: https://github.com/getpaseo/paseo/discussions
+    about: Same conversation, on GitHub. Issues are only for bugs, and feature requests opened as issues get closed automatically.