fix: tighten vague language across all prompt files

- Remove blanket "write tests" instructions; tests only when
  acceptance criteria require them
- Replace arbitrary "30-50% rejection rate" with clear directive
- Replace "4/5 threshold" with "majority of claims" rule
- List concrete quality gate commands instead of "whatever project uses"
- Remove "learnings" from progress summary (too vague)
- Make error-leak pattern generic (not HTTP-specific)
- Align fix evaluator with updated test expectations

prompts/generator/implement.md

@@ -16,7 +16,7 @@ You are building features from a PRD. Each story is a small, self-contained unit
 
 - **Minimal changes only.** Do not refactor surrounding code or add features beyond scope.
 - **Follow the contract's Out of Scope section.**
-- **If tests don't exist yet,** write them as part of the story.
+- **Write tests only if the story's acceptance criteria require them.**
 - **If you need a dependency,** install it and note it in progress.md.
 
 ## Git