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.

docs/glossary.md

@@ -41,6 +41,7 @@ Authoritative terminology. UI label wins. Don't invent synonyms; use what's here
 - **Subagent** — User-facing term for an agent session related to a parent agent session. Use **subagents** in UI copy and docs. Internal daemon/provider plumbing may say "child agent" or `child_session`, especially for provider-managed imports; do not surface "child agent" as a product term.
 - **Attachment tray** — The selected-attachments row inside the composer input, above the text input. Code: `renderAttachmentTray` (`packages/app/src/composer/index.tsx`). Forbidden: "Attachment bar".
 - **Conflict** — Two distinct senses; do NOT use the bare word in UI copy without qualifying which: (a) **stale-write conflict** on `paseo.json` ("Config changed on disk", code `stale_project_config`, `packages/app/src/screens/project-settings-screen.tsx:593`); (b) **git merge conflict** (no current UI string).
+- **Product discussion** — Where non-bug product talk goes: [GitHub Discussions](https://github.com/getpaseo/paseo/discussions) and `#product` in Discord. Covers workflows, features, and product direction. The container term; the ask inside it is always a **workflow** — what you're doing, how you do it today, where Paseo gets in the way. Issues are bugs only. Forbidden: "Feature request" as a Paseo surface, label, or invitation; the phrase is only used when answering someone who arrived with it. Don't invent "feature discussion", "idea", or "workflow thread" as synonyms. See [CONTRIBUTING.md](../CONTRIBUTING.md).
 
 ## Inconsistencies (documented, not papered over)