docs(stack-encrypt): say which target carries the json index

The target descriptor's table said a type's indexes include `json` for a
SteVec document. The v4 target table no longer has a SteVec row; the one
type carrying the JSON index is the document family's stored type,
`JsonSearch`, as eql-bindings' own table says.

Claude-Session: https://claude.ai/code/session_01HLuZxys1NDRmAkv3uhnuoJ

Author: coderdan

packages/stack-encrypt/src/dynamic/target.rs

@@ -51,7 +51,7 @@ use crate::{KeysetCipher, Label, Pending, StackCipher};
 /// | `suffix` | string: the query-capability suffix, `Eq`; empty for a storage-only type |
 /// | `plaintext` | string or null: the [`ValueKind`] name the type is produced from — the same names a field's `"type"` key uses — or null while unspecified |
 /// | `sql_domain` | string: the stored value's PostgreSQL domain |
-/// | `indexes` | list of strings: the indexes the type carries, by `IndexSpec::key()`, plus `json` for a SteVec document |
+/// | `indexes` | list of strings: the indexes the type carries, by `IndexSpec::key()`: `eq`, `match`, `ore`, `ope`, and `json` for a document family's stored type (`JsonSearch`) |
 /// | `query` | string or null: the query twin's type name |
 /// | `query_sql_domain` | string or null: the query twin's PostgreSQL domain |
 /// | `producible` | bool: whether the engine produces the type today |