docs(agents): add member-to-free-function refactoring pattern

Capture the incremental refactoring workflow validated in the DFTU
occupancy-matrix refactor: inventory this-> reads, pass them as
explicit parameters (const for config, reference for mutable state),
move the function only when the body is this-free, keep a thin
wrapper at the old entry point, and compile each step.

Author: abacus_fixer

AGENTS.md

@@ -84,6 +84,12 @@ rules. Read the complete governance document before making or reviewing changes:
 - Exceptions must be recorded in the PR with reason, scope, risk, and a follow-up
   cleanup plan.
 
+## Refactoring Patterns
+
+- Member -> free function: inventory `this->` reads; pass as params (const
+  for config, ref for mutable state); move only when body is `this`-free;
+  keep thin wrapper; compile each step.
+
 ## Local Commands
 
 ```bash