chore(skills): name directExecution as retired in the add-integration checklist (#7236)

The transport checklist listed the property inside a bare enumeration --
"declares `request.internal`, or `directExecution`, or has an HTTP fallback" --
which stacks two disjunctions and drops the "retired" framing every other
statement of this rule carries, including line 71 of the same file and the
add-tools, add-trigger, and add-block skills. A reader scanning the checklist
could take it for a property that still exists and is merely discouraged.

Wording only; the rule itself is unchanged and is enforced by
check:tool-request-boundary.

Author: waleedlatif1

.agents/skills/add-integration/SKILL.md

@@ -606,8 +606,8 @@ If creating V2 versions (API-aligned outputs):
 - [ ] Created tool file for each operation
 - [ ] Chose exactly one boundary per tool: registered `InternalToolConfig.operation` or absolute
       external HTTP(S) `ToolConfig.request`
-- [ ] No tool points to `/api/...`, constructs a URL back to Sim, declares `request.internal`, or
-      `directExecution`, or has an HTTP fallback for an in-process operation
+- [ ] No tool points to `/api/...`, constructs a URL back to Sim, declares `request.internal` or the
+      retired `directExecution` property, or has an HTTP fallback for an in-process operation
 - [ ] All params have correct visibility
 - [ ] All nullable fields use `?? null`
 - [ ] All optional outputs have `optional: true`