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-governance-layer.sh

@@ -83,9 +83,9 @@ echo "--- Supporting docs ---"
   && pass "docs/ai-constitution.md exists" \
   || fail "docs/ai-constitution.md missing"
 
-[[ -f "$REPO_ROOT/docs/HUMANS.md" ]] \
-  && pass "docs/HUMANS.md exists" \
-  || fail "docs/HUMANS.md missing"
+[[ -f "$REPO_ROOT/docs/wiki/HUMANS.md" ]] \
+  && pass "docs/wiki/HUMANS.md exists (moved to wiki)" \
+  || fail "docs/wiki/HUMANS.md missing"
 
 [[ ! -f "$REPO_ROOT/docs/research/governance_principles/ai-constitution.md" ]] \
   && pass "ai-constitution.md removed from research folder (moved to docs/)" \