feat: add concrete examples of good vs bad acceptance criteria

Planner now sees specific examples of verifiable criteria (grep,
test commands, file checks) alongside vague anti-patterns. Drives
higher story quality which directly improves evaluator accuracy.

prompts/planner/plan.md

@@ -16,7 +16,19 @@ A story must be completable in a single iteration. Keep each story focused — a
 If a story fails (evaluator rejects it), the next iteration should be able to retry it cleanly. Stories with too many moving parts are hard to retry because partial state is messy.
 
 ### Evaluability
-Every story must have criteria the evaluator can independently verify. "The code is clean" is not evaluable. "The function returns 404 when the user doesn't exist" is evaluable.
+Every story must have criteria the evaluator can independently verify by reading code, running commands, or testing behavior.
+
+Good criteria are specific and checkable:
+- "Grep for 'HARDCODED_KEY' returns zero matches"
+- "The function returns 404 when the user doesn't exist"
+- "Running `npm test` passes with no failures"
+- "The config file contains entries for all three required env vars"
+
+Bad criteria are vague or subjective:
+- "The code is clean"
+- "Works correctly"
+- "Performance is improved"
+- "Error handling is robust"
 
 ## PRD Anti-Patterns