test: update stale file-existence checks after PRD and HUMANS.md moves

## Why
Two test suites were asserting on paths that were intentionally changed:
- docs/HUMANS.md moved to docs/wiki/HUMANS.md (wiki submodule)
- docs/prd/ deleted after migrating all PRDs to Gitea (#16–#19)

Updated checks to assert the new locations and confirm the old
directories are gone.

---
Refs: #15

tests/test-instructions-and-docs.sh

@@ -158,15 +158,15 @@ echo ""
 
 echo "--- 0008: docs/ restructure ---"
 
-for dir in prd notes adr; do
+for dir in notes adr; do
   [[ -d "$REPO_ROOT/docs/$dir" ]] \
     && pass "docs/$dir/ exists" \
     || fail "docs/$dir/ missing"
 done
 
-[[ -f "$REPO_ROOT/docs/prd/chunk-1.md" ]] \
-  && pass "docs/prd/chunk-1.md exists (migrated)" \
-  || fail "docs/prd/chunk-1.md missing"
+[[ ! -d "$REPO_ROOT/docs/prd" ]] \
+  && pass "docs/prd/ deleted (migrated to Gitea)" \
+  || fail "docs/prd/ still exists — should have been deleted after Gitea migration"
 
 [[ ! -f "$REPO_ROOT/docs/prd-chunk-1.md" ]] \
   && pass "docs/prd-chunk-1.md removed from docs root" \