fix(32): WR-07 close the relation and partial routes of hidden owner fields

Hide removed an owner field from the schema, show and save, but a hidden
relation-manager field's relation routes (panel, link, unlink, child CRUD,
deferred commit) and a hidden partial field's partial stayed reachable.
dropHiddenFields now drops the relation and the partial path too; a partial
the list or preview header or another field still uses keeps rendering.

docs/backend/admin-controllers.md

@@ -600,7 +600,7 @@ Every field and tab of a compiled form has a stable name: the field key, and the
 - A new tab is declared under `tabs:` and goes `after:` or `before:` an anchor tab, or after the last tab without one. `after: default` is allowed; `before: default` stops the boot, because the admin always renders the default tab first. A form without tabs that gains one renders its own fields under the default tab ("Basic"), then the new tab.
 - `zone:` takes `tabs` (the default) only for now. `outside` and `secondary` (`pact.AdminFormZoneOutside`, `pact.AdminFormZoneSecondary`) are reserved and stop the boot with "is not supported yet".
 - Extensions apply in plugin activation order (`Requires()` first). Several extensions anchored at the same point keep that order. An anchor may name a field or tab another plugin's extension added only when that plugin is in the contributor's `Requires()`; the fields of one document may anchor on each other in any order.
-- `Hide` lists owner fields to leave out of the form for every administrator: they leave the schema, the record and the save, and a tab that loses all its fields disappears. The owner's model must not require a hidden field.
+- `Hide` lists owner fields to leave out of the form for every administrator: they leave the schema, the record and the save, a hidden `relation-manager` field's relation routes (panel, link, unlink, child records) and a hidden `partial` field's partial answer 404 (a partial the list or preview header or another field still uses keeps rendering there), and a tab that loses all its fields disappears. The owner's model must not require a hidden field.
 - cabana compiles the order once at boot and sends the fields in that order. A form an extension lays out is regrouped by tab in first-appearance order, the default tab first, exactly as the admin renders tabs; a form no extension lays out (including one that only gets a `Save` hook) is compiled byte for byte as before. The admin renders what it receives and adds no ordering of its own, and `span` (left, right, full) keeps working next to inserted fields.
 - Only top-level fields and tabs are placed; fields inside repeaters stay the owner's.