fix: final 4 pre-existing test bugs — 184/0, 0 failures

- literate: test-block-balance-check-valid path defaults to
  PASSEPARTOUT_DATA_DIR (installation dir), not MEMEX_DIR (dev clone)
- diagnostics: use symbol-value+find-symbol to access jailed-package
  variables (*diagnostics-binaries*), avoiding stale symbol conflict
- archivist: add fiveam: prefix to all test macros (prevents suite
  cross-contamination when loaded via skill system); fix :if-exists
  :nil parsing bug in archivist-create-note; fix ~% literal chars
- llm-gateway: cross-contamination resolved by archivist fiveam: prefix
  fix; test-archivist-create-note no longer leaks into llm-gateway-suite

Result: 25 suites, 184 checks, 0 failures (was 80P 16F → 180P 4F → 184P 0F)

org/programming-literate.org

@@ -131,8 +131,7 @@ contents of the Lisp file. Returns T if they match, or an error message."
   (is (eq t (literate-block-balance-check
              (merge-pathnames "org/core-loop.org"
                               (uiop:ensure-directory-pathname
-                               (or (uiop:getenv "MEMEX_DIR")
-                                   (namestring (user-homedir-pathname)))))))))
+                               (uiop:getenv "PASSEPARTOUT_DATA_DIR")))))))
 
 (test test-block-balance-check-missing-close
   "Contract 2: unbalanced parens return non-T."