fix: list tolerates a null _id; declare the cryptography dependency

A stored doc with a present-but-null _id crashed the whole list table: doc.get('_id',
'')[:16] slices None (the '' default only applies when _id is absent), so one bad doc
aborted the render - now uses (doc.get('_id') or '')[:16], mirroring revoke's finder, so
it renders a blank placeholder row. cli.py imports cryptography.exceptions.InvalidTag but
pyproject only pulled cryptography transitively via envelope_crypto - declare it directly.

Signed-off-by: disqualifier <dev@disqualifier.me>

src/envelope_authorizer/commands/list_keys.py

@@ -40,7 +40,7 @@ def run(config, storage, args) -> None:
     for doc in docs:
         meta = doc_meta(doc)
         print(
-            f"{doc.get('_id', '')[:16]:<18} "
+            f"{(doc.get('_id') or '')[:16]:<18} "
             f"{str(meta.get('friendly', '-')):<16} "
             f"{str(meta.get('created_by', '-')):<18} "
             f"{_created(meta):<21} "