chore: let this repo's own reviewers rate design findings by cost

.expo-agents/code-review/agents/correctness.md

@@ -42,7 +42,8 @@ issues in the changed code.
 - Style or formatting concerns handled by a linter/formatter.
 - Issues in unchanged code the PR does not touch.
 - "Consider using library X instead" suggestions.
-- Theoretical concerns with no concrete failure path.
+- Theoretical concerns with no concrete failure path (or, for a `design`
+  finding, no concrete cost).
 - Nitpicks about naming or idiom when the existing convention is being followed.
 - Anything a type-checker or linter would already catch.
 

.expo-agents/code-review/shared.md

@@ -122,6 +122,10 @@ For every real finding, assess two separate dimensions:
   - `Low` — a bounded edge case with little correctness or safety effect. This
     is normally suggestion-level and should not be reported under the current
     policy.
+- **A `design` finding** has a concrete cost instead of a failure path. Its
+  `Confidence` is how directly the code shows that cost, and its `Impact if
+  shipped` is how large the cost is. A design cost that is only `Low` is a
+  `suggestion`.
 
 Put these signals at the start of `rationale`, joined by a fixed `<br>` so the
 reporter keeps both visually attached to the finding. Follow them with the