refactor(db): GetCollectionItemsForDashboard embeds the media row; excluded filter moves into SQL; third converter dies

SELECT mi.*, ci.excluded forced every caller to filter tombstone
exclusions in Go over a 69-field row, then a 45-field hand converter
(getCollectionItemsRowToMediaItems) copied it field-by-field into
MediaItems for BuildSections. The query now filters
(ci.excluded IS NOT TRUE) itself and returns sqlc.embed(mi) — callers
consume .MediaItems directly, the Go filter loops die in both
collection-detail ladders (JSON + SSR), and the converter is deleted.

Pins, H1/H3 tests, unit suites green.

internal/handlers/cards.go

@@ -125,20 +125,21 @@ func BookCardsFromMediaItems(rows []database.MediaItems, libTypes map[string]str
 }
 
 // BookCardsFromCollectionDashRows builds cards from the
-// collection-items join (GetCollectionItemsForDashboard). The row's ID
-// IS the media item id. The Excluded filter stays at call sites — only
-// the two collection-detail surfaces exclude tombstones.
+// collection-items join (GetCollectionItemsForDashboard). The query
+// embeds the media row and filters excluded rows in SQL, so the adapter
+// reads through the embed.
 func BookCardsFromCollectionDashRows(rows []database.GetCollectionItemsForDashboardRow, libTypes map[string]string) []BookInfo {
 	cards := make([]BookInfo, 0, len(rows))
 	for _, r := range rows {
+		mi := r.MediaItems
 		cards = append(cards, buildBookCard(cardSource{
-			ID:          uuid.UUID(r.ID.Bytes),
-			Title:       r.Title,
-			Author:      utils.PgTextString(r.Author),
-			LibraryID:   r.LibraryID,
-			CoverPath:   r.CoverImagePath,
-			FormatGroup: r.FormatGroup,
-			LibraryType: libTypes[uuid.UUID(r.LibraryID.Bytes).String()],
+			ID:          uuid.UUID(mi.ID.Bytes),
+			Title:       mi.Title,
+			Author:      utils.PgTextString(mi.Author),
+			LibraryID:   mi.LibraryID,
+			CoverPath:   mi.CoverImagePath,
+			FormatGroup: mi.FormatGroup,
+			LibraryType: libTypes[uuid.UUID(mi.LibraryID.Bytes).String()],
 		}))
 	}
 	return cards