Clean up bundleless context item follow-ups
Follow-up to:
- #3584775+s
- #3586220+s
## Description
Follow-up after bundle removal (#3584775) and the context item full view MR
(#3586220). Most bundle-less reconciliation was already on `1.0.x`; this MR
closes the remaining gaps found during review.
## Changes
### 1. Drop bundle theme suggestions
`hook_theme_suggestions_ai_context_item()` now adds only view-mode
suggestions (e.g. `ai_context_item__full`). Removed bundle-based suggestions
that referenced `$entity->bundle()`.
### 2. Fix context item edit form field order
**Root cause:** `purpose` and `content` both used form weight `2`, so content
appeared before purpose when weights tied.
**Fix:**
- `AiContextItem.php` — form weights: purpose `3`, content `4`; content view
weight `3`.
- `core.entity_form_display.ai_context_item.ai_context_item.default.yml` —
aligned install weights:
| Weight | Field |
|--------|-------|
| 0 | label |
| 1 | langcode |
| 2 | description |
| 3 | purpose |
| 4 | content |
| 5 | subcontext_type |
| 6 | parent |
| 7 | tags |
| 10 | moderation_state |
| 20 | uid |
| — | status (hidden) |
No update hook for existing site form displays (beta).
### 3. Remove stale bundle keys from tests
Removed obsolete `'type' => 'default'` from `AiContextItem::create()` calls in
six kernel tests. The entity is bundleless; those keys were silently ignored
but misleading.
- `AiContextUsageTrackerTest`
- `AiContextScopeEntityTest`
- `AiContextConditionalSubcontextE2ETest`
- `AiContextTextFieldMigrationTest`
- `AiContextItemFormGlobalCountTest`
- `AiContextDocumentLoaderIntegrationTest`
## Already on `1.0.x` (not in this MR)
- Full view display install config and `ai_context_update_10010()` legacy
migration
- View tests without `ai_context_item_type` / `'type' => 'default'`
- View builder, templates, routes, preprocess — already bundle-agnostic
## Testing
- `./lint.sh`
- View-related kernel/functional tests
- Kernel tests updated in item 3
## AI usage
- [x] AI assisted issue
- [x] AI generated code
issue