docs(content): a tree field does not require reference — two pages said it did (#14890)

`reference` is required for `lookup` and `master_detail` only. Three surfaces
already agree on that and two docs pages disagreed with all three:

- `packages/spec/src/data/field.zod.ts:1064-1065` (the `reference` docblock)
  names `lookup` and `master_detail` as the types the superRefine enforces it for.
- `packages/spec/src/data/field.zod.ts:1073` (`.describe()`) says "Target object
  name (snake_case) for lookup/master_detail fields".
- `packages/lint/src/data-model-rules.ts:103` —
  `RELATIONSHIP_TYPES = new Set(['lookup', 'master_detail'])`, consumed at :499
  and :577 by `relationship/missing-reference`. `tree` is not in the set.

A reference-less `tree` is a shape the spec's own tests construct and assert
defined behaviour for — `field-value.test.ts:69` (`referenceTargetOf` returns
undefined) and `filter-dotted-head.test.ts:31` (still classified `relation`) —
so no gate rejects one and none should: the docs were asserting a requirement
nothing enforces. A default-self-reference reading is falsified too, by
`examples/app-showcase/src/data/objects/field-zoo.object.ts:108`, where a `tree`
field points at `showcase_category` rather than at its own object.

Two cells, both stating the same claim:

- `content/docs/deployment/troubleshooting.mdx:78` drops `tree` from the symptom
  line. The Cause line at :80 stays true for the two remaining types.
- `content/docs/data-modeling/validation-rules.mdx:542` — the "Quick Validation
  Summary" table's second column is `Required Props` (:517), and the `tree` row
  listed `reference` there. It becomes an em dash, matching the `user` row beside
  it, which is likewise a reference-carrying type with no required prop.


Claude-Session: https://claude.ai/code/session_017RbbUMnxkUnWhE4j94v8FE

Co-authored-by: Claude <noreply@anthropic.com>

Author: claude[bot]

content/docs/data-modeling/validation-rules.mdx

@@ -539,7 +539,7 @@ section above). See the
 | `lookup` | `reference` | Foreign key integrity |
 | `user` | — | Lookup specialized to `sys_user`; `multiple: true` stores an id array |
 | `master_detail` | `reference` | Cascade delete, ownership |
-| `tree` | `reference` | Self-referencing; no automatic cycle check |
+| `tree` | — | Self-referencing; no automatic cycle check |
 | `image` | — | Common image MIME types; `multiple` for many |
 | `file` | — | Any file type; `multiple` for many (no field-level upload config) |
 | `avatar` | — | Single image, typically square |

content/docs/deployment/troubleshooting.mdx

@@ -75,7 +75,7 @@ The custom error map provides "Did you mean?" suggestions for common typos.
 
 ### "Required property missing: reference"
 
-**Symptom:** A `lookup`, `master_detail`, or `tree` field fails validation.
+**Symptom:** A `lookup` or `master_detail` field fails validation.
 
 **Cause:** Relational fields require a `reference` property pointing to the target object.