refactor: remove unnecessary type conversions and handle ignored errors across codebase

Remove redundant type conversions that Go 1.26 makes unnecessary or that
were already no-ops:

- uuid.UUID(x.Bytes) → x.Bytes (uuid.UUID is [16]byte, same as pgtype UUID Bytes)
- pgtype.UUID{Bytes: [16]byte(u), Valid: true} → pgtype.UUID{Bytes: u, Valid: true}
- (*time.Time)(&x.Time) → &x.Time
- json.RawMessage(x) → x where x is already []byte
- []byte(stringVal) → stringVal where []byte is expected
- int()/int64()/byte() casts on values already of the target type
- Decompressor(fn) → fn (type is identical)

Handle previously ignored error returns:

- collections.go: check json.Unmarshal error in GetCollection
- conversion_service.go: check fileSize.Scan() error
- app_test.go: check app.Shutdown() error in benchmark

internal/services/conversion_service.go

@@ -12,6 +12,7 @@ import (
 	"time"
 
 	"bookhoard/internal/database"
+
 	"github.com/jackc/pgx/v5/pgtype"
 )
 
@@ -81,7 +82,10 @@ func (s *ConversionService) ConvertEPUBToKEPUB(ctx context.Context, mediaItemID
 	}
 
 	var fileSize pgtype.Int8
-	fileSize.Scan(int64(fileinfo.Size()))
+	err = fileSize.Scan(fileinfo.Size())
+	if err != nil {
+		return nil, err
+	}
 
 	_, err = s.db.CreateMediaItemFormat(ctx, database.CreateMediaItemFormatParams{
 		MediaItemID:           mediaItemID,

internal/services/dashboard_service.go

@@ -154,7 +154,7 @@ func (s *DashboardService) GetDashboardSections(
 		}
 
 		results = append(results, DashboardSection{
-			CollectionID:   uuid.UUID(coll.ID.Bytes),
+			CollectionID:   coll.ID.Bytes,
 			CollectionName: coll.Name,
 			Items:          items,
 			QueryType:      coll.QueryType.String,
@@ -182,7 +182,7 @@ func (s *DashboardService) GetDashboardSections(
 		}
 
 		results = append(results, DashboardSection{
-			CollectionID:   uuid.UUID(coll.ID.Bytes),
+			CollectionID:   coll.ID.Bytes,
 			CollectionName: coll.Name,
 			Items:          items,
 			QueryType:      coll.QueryType.String,

internal/services/media_scanner.go

@@ -1536,7 +1536,7 @@ func (s *MediaScanner) extractEPUBCover(epubPath string) (string, error) {
 			opfStartAttr += len("full-path=")
 			quote := content[opfStart+opfStartAttr]
 			opfStartQuote := opfStart + opfStartAttr + 1
-			opfEndQuote := bytes.Index(content[opfStartQuote:], []byte{byte(quote)})
+			opfEndQuote := bytes.Index(content[opfStartQuote:], []byte{quote})
 			if opfEndQuote == -1 {
 				continue
 			}

internal/services/reader.go

@@ -383,7 +383,7 @@ func (s *ReaderService) UpdateSettings(
 	// Update in database
 	_, err = s.db.UpsertReaderSettings(ctx, database.UpsertReaderSettingsParams{
 		UserID:       pgtype.UUID{Bytes: userID, Valid: true},
-		SettingValue: []byte(settingsJSON),
+		SettingValue: settingsJSON,
 	})
 
 	return err