docs(agents): add mandatory UAT rule + fix .crush prune in check-rules

- UAT rule: user must accept work before done-ratio 100% or close
- check-rules.sh: prune .crush/ from Discourse pointer scan (agent
  working space, not documentation)

💘 Generated with Crush

Assisted-by: Crush:glm-5.2

AGENTS.md

@@ -46,6 +46,13 @@ There are no exceptions to this rule.**
    it's ambiguous whether the work is truly complete, don't suggest a
    close — leave that decision to the user. This applies to ALL tickets,
    no exceptions.
+8. **User acceptance testing is MANDATORY before declaring work done.**
+   The agent performs implementation and technical validation (services
+   running, configs correct, APIs responding). The user performs UAT —
+   visually confirming dashboards render data, alerts deliver, tools are
+   usable. The agent MUST NOT set done-ratio to 100%, MUST NOT suggest
+   closing, and MUST NOT move to the next ticket until the user explicitly
+   accepts the work. "Technically wired but blank dashboard" is NOT done.
 
 ### Access-channel policy: SSH only (NON-NEGOTIABLE)