Fix alphabet highlight for names starting with "The " (#1788)

## Description
The alphabet scroll bar highlighted the letter of an item's *display*
name while the grid sorted by the server's article-stripped `SortName`,
so "The Beatles" sat under **B** but highlighted **T**.

- **Artists:** the Artists tab never requested `SortName`, so the
highlight silently fell back to `Name`. It now asks for `SlimItemFields`
(which already includes `SORT_NAME`), matching the sibling `/Items`
branch. The count-only query used for letter positions passes `fields =
null`, since a `limit = 0` request has no use for them.
- **Genres and studios:** these grids bucketed on the display name
unconditionally. The sort-name fallback is extracted as
`BaseItemDto.alphabetSortName` (`sortName ?: name ?: ""`) and carried
onto the `Genre` and `Studio` grid items, so all three grids now derive
the letter from one value.

### Related issues
https://github.com/damontecres/Wholphin/issues/1787

### Testing
Two unit tests added:
- `CollectionFolderViewModelTest` pins that the artist pager actually
requests `SORT_NAME` — the field whose absence caused the bug.
- `AlphabetSortNameTest` covers both branches of the `alphabetSortName`
fallback.

Manually: select a music library → Artists tab → put the cursor on an
artist starting with "The " and confirm the highlighted letter matches
the grid position. Same check on the genre and studio grids.

## AI or LLM usage
I used Cursor for debugging and implementing the fix, and Claude Code
for a follow-up cleanup pass over the diff.

app/src/main/java/com/github/damontecres/wholphin/data/model/BaseItem.kt

@@ -54,7 +54,7 @@ data class BaseItem(
         get() = type.playable
 
     override val sortName: String
-        get() = data.sortName ?: data.name ?: ""
+        get() = data.alphabetSortName
 
     val type get() = data.type
 
@@ -305,6 +305,9 @@ data class BaseItem(
 
 val BaseItemDto.aspectRatioFloat: Float? get() = width?.let { w -> height?.let { h -> w.toFloat() / h.toFloat() } }
 
+/** The server strips leading articles (eg "The ") from [BaseItemDto.sortName]. */
+val BaseItemDto.alphabetSortName: String get() = sortName ?: name ?: ""
+
 @Immutable
 data class BaseItemUi(
     val episodeCornerText: String?,

app/src/main/java/com/github/damontecres/wholphin/ui/components/CollectionFolderView.kt

@@ -399,6 +399,7 @@ class CollectionFolderViewModel
                 GetArtistsRequest(
                     parentId = item?.id,
                     enableImageTypes = listOf(ImageType.PRIMARY, ImageType.THUMB),
+                    fields = SlimItemFields,
                 ),
             )
         }
@@ -477,6 +478,7 @@ class CollectionFolderViewModel
                         GetArtistsHandler.countMatching(
                             createGetArtistsRequest(filter).copy(
                                 enableImageTypes = null,
+                                fields = null,
                                 nameLessThan = letter.toString(),
                                 limit = 0,
                                 enableTotalRecordCount = true,

app/src/main/java/com/github/damontecres/wholphin/ui/components/GenreCardGrid.kt

@@ -20,6 +20,7 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import com.github.damontecres.wholphin.data.ServerRepository
 import com.github.damontecres.wholphin.data.model.BaseItem
+import com.github.damontecres.wholphin.data.model.alphabetSortName
 import com.github.damontecres.wholphin.data.model.createGenreDestination
 import com.github.damontecres.wholphin.services.ImageUrlService
 import com.github.damontecres.wholphin.services.NavigationManager
@@ -104,7 +105,12 @@ class GenreViewModel
                             .execute(api, request)
                             .content.items
                             .map {
-                                Genre(it.id, it.name ?: "", null)
+                                Genre(
+                                    id = it.id,
+                                    name = it.name ?: "",
+                                    imageUrl = null,
+                                    sortName = it.alphabetSortName,
+                                )
                             }
                     _state.update {
                         it.copy(
@@ -243,10 +249,10 @@ data class Genre(
     val id: UUID,
     val name: String,
     val imageUrl: String?,
+    override val sortName: String = name,
 ) : CardGridItem {
     override val gridId: String get() = id.toString()
     override val playable: Boolean = false
-    override val sortName: String get() = name
 }
 
 /**

app/src/main/java/com/github/damontecres/wholphin/ui/components/StudioCardGrid.kt

@@ -20,6 +20,7 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import com.github.damontecres.wholphin.data.ServerRepository
 import com.github.damontecres.wholphin.data.model.BaseItem
+import com.github.damontecres.wholphin.data.model.alphabetSortName
 import com.github.damontecres.wholphin.data.model.createStudioDestination
 import com.github.damontecres.wholphin.services.ImageUrlService
 import com.github.damontecres.wholphin.services.NavigationManager
@@ -97,7 +98,12 @@ class StudioViewModel
                                         imageType = ImageType.THUMB,
                                         fillWidth = cardWidthPx,
                                     )
-                                Studio(it.id, it.name ?: "", imageUrl)
+                                Studio(
+                                    id = it.id,
+                                    name = it.name ?: "",
+                                    imageUrl = imageUrl,
+                                    sortName = it.alphabetSortName,
+                                )
                             }
                     _state.update {
                         it.copy(
@@ -133,10 +139,10 @@ data class Studio(
     val id: UUID,
     val name: String,
     val imageUrl: String?,
+    override val sortName: String = name,
 ) : CardGridItem {
     override val gridId: String get() = id.toString()
     override val playable: Boolean = false
-    override val sortName: String get() = name
 }
 
 data class StudioGridState(