fix(spec): align config-schema.json object ownership with the record-ownership vocabulary

`packages/spec/config-schema.json` declared the object-level `ownership`
property as `enum ["own", "shared"]`. That matched neither vocabulary in the
package: the record-ownership model is `user | business_unit | org | none`
(`packages/spec/src/data/object.zod.ts`, post-#7260), and the package
*contribution* kind is own/extend/overlay and lives on the registry's
contributor record, not on the object schema. `["own","shared"]` was a stale
third spelling with no acceptance face behind it.

This artifact is hand-written authoring guidance served to config authors as
IDE autocomplete/validation, so the entry actively steered an author toward
`ownership: "shared"` — a value no schema in the package accepts (#3244
confusion class: same key name, different vocabularies, adjacent surfaces).

Aligns the enum to the acceptance face and adopts its `.describe()` text,
whose closing sentence carries the own/extend disambiguation that caused the
drift. The acceptance face itself is untouched — `object.zod.ts` is
byte-identical to `origin/main`.

Fixes #7286

Author: os-help

packages/spec/config-schema.json

@@ -66,8 +66,8 @@
           },
           "ownership": {
             "type": "string",
-            "enum": ["own", "shared"],
-            "description": "Record ownership model"
+            "enum": ["user", "business_unit", "org", "none"],
+            "description": "Record-ownership model: user (default — injects reassignable owner_id plus owning_business_unit_id) | business_unit (unit-owned: owning_business_unit_id only, no owner_id) | org | none (no per-record owner, neither anchor). Distinct from the package own/extend contribution kind."
           },
           "fields": {
             "type": "object",