Admin: Reject non-primitive itemLabel property values

[lehni]

Written by Claude.

getItemLabel (packages/admin/src/mixins/ItemMixin.js) has a property-key fallback that takes whatever item[key] returns:

const key = (
  isString(itemLabel) && itemLabel ||
  isListSource(sourceSchema) && columns && Object.keys(columns)[0] ||
  'name'
)
text = item[key]   // could be anything — array, object, function

The implicit contract is "produces a value usable as the label prop on DitoFormInner (typed String)", but nothing enforces it. If the property happens to hold an Array or Object — easy when the model property name and itemLabel collide — that flows into the Vue prop. Vue's prop validation then runs String(reactive proxy), throws Cannot convert object to primitive value, and the form render dies silently. Symptom we hit: e2e/assets/admin/upload.ts:29 'single file appears in table' reproduces the form mounting empty (<form><div class="dito-schema"><!--v-if--></div></form>).

Fix

Only accept string and number from the property lookup; otherwise fall through to the auto-generated label (index, etc.):

const value = item[key]
text = isString(value) || isNumber(value) ? value : null

Verified

The assets test schema uses itemLabel: 'files', which collides with AssetWidget.files. Before this PR, that produces a 100% reproducible failure on e2e/assets/admin/upload.ts:29. After this PR:

• pnpm --filter @ditojs/tests test:e2e cold cache: 59/59 passing in 21.6s
• The schema rename in PR Tests: Rename assets itemLabel to avoid collision with property key #174 is no longer needed; that PR can be closed in favor of this one.

Test plan

• Run pnpm --filter @ditojs/tests test:e2e — full suite green
• Sanity-check existing admin scenarios that already use string-typed itemLabel properties — no behavior change expected