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/evaluator/implement.md

@@ -17,4 +17,4 @@ You are evaluating an implementation story. The generator claims to have built a
 - Code exists but doesn't actually run
 - Removed an import or variable during refactoring but it's still used elsewhere in the file
 - New instance of a shared resource (e.g., DB connection, rate limiter) instead of using the existing one
-- Error details leaked to HTTP responses (use logging server-side, return generic message to client)
+- Internal error details (stack traces, exception messages) exposed in user-facing output instead of being logged server-side