feat(sandcastle): implementer + reviewer prompts include fallow audit

.sandcastle/reviewer.prompt.md

@@ -31,6 +31,7 @@ If you suspect the implementer hand-rolled what should have been generator outpu
 3. **Manifest-first ordering**: if a new use case landed, the manifest was updated; tests exist; the factory was wrapped at bind time.
 4. **Conformance gates**: the diff's tests + lint + typecheck pass. (You don't run them yourself; sandcastle's CI step does. Trust the CI status, reject if it's red.)
 5. **Generator-first**: see the section above. Hand-rolled code that should have been generated is a rejection.
+6. **Fallow audit**: verify the implementer ran `pnpm fallow:audit` and it passed. If their diff increases dead exports / dupes / circular deps / complexity beyond the baseline, that's a rejection cause unless the implementer's notes explicitly justify it.
 
 ## Output format