json_tree is missing from the EQL catalog, so no Go types are generated for it #1348

Background

json_tree is the EQL v4 type family for an encrypted JSON document. EQL (Encrypt Query Language) is the SQL library installed into a customer's PostgreSQL database; Stack Encrypt is the Rust engine that encrypts the values EQL stores. The Rust engine and the SQL for json_tree are built in #1288, #1325, #1329 and #1336.

Every EQL type is listed in one catalog. eql-codegen reads that catalog to generate the Rust target table and the Go types in languages/golang/encrypt/eql/eql_gen.go. A Go program stores and queries EQL columns through those generated types.

Problem

The json_tree types were hand-written in packages/eql/crates/eql-bindings/src/v4/json_tree.rs and never added to the catalog. That file says so itself: the family is "not in the catalog yet, so it is not in super::all nor in the target table".

So:

• the Go SDK has no eql.JSONTree type to scan a column into;
• the engine's guest cannot look the type up by name;
• stashgen cannot see that a json_tree field must use null=sql. A null document cannot be padded to a value's length, because documents have no single length.

Proposal

1. Add the json_tree family to the catalog, v4::all() and the target table: the stored type, the query type, the leaf query type and the entry type.
2. Run mise run types:generate, so eql_gen.go gains JSONTree, JSONTreeQuery, JSONTreeLeafQuery and JSONTreeEntry. Each is marked not producible, with a reason that points at the data-plan issue.
3. Decide whether the selector, which is a text value, needs a generated or a hand-written Go type.
4. Report the family as not fixed-width, so stashgen requires null=sql.
5. Gates: types:check, go_eql_parity and the eql-codegen tests.

Plan: docs/plans/2026-10-24-go-json-tree.md, step 1.