fix(scanner): classify .docx as reflowable — was landing format_group unknown

.docx is accepted for ingest but the format-group switch had no case
for it, so every DOCX row stored format_group 'unknown' with
is_reflowable=false. Extract the classification switch into a pure
classifyFormatGroup helper with a table test, and classify .docx
reflowable like the other reflowable text formats (.rtf/.doc stay out
until they are readable client-side). Existing rows: dev alice (DOCX)
reclassified by hand; production rows reclassify on rescan.

internal/services/media_scanner.go

@@ -974,30 +974,12 @@ func (s *MediaScanner) processMediaFile(ctx context.Context, path string) (bool,
 	// Set format group, total characters, and chapter count
 	mimeType := s.getMimeType(path)
 	ext := strings.ToLower(filepath.Ext(path))
-	var formatGroup string
-	var isReflowable, hasFixedLayout bool
-	switch ext {
-	case ".epub":
+	var epubIsFixedLayout bool
+	if ext == ".epub" {
 		isFixed, fixedErr := s.DetectFixedLayoutEPUB(path)
-		if fixedErr == nil && isFixed {
-			formatGroup = "fixed_layout"
-			hasFixedLayout = true
-		} else {
-			formatGroup = "reflowable"
-			isReflowable = true
-		}
-	case ".mobi", ".azw", ".azw3", ".fb2", ".txt":
-		formatGroup = "reflowable"
-		isReflowable = true
-	case ".pdf", ".djvu":
-		formatGroup = "fixed_layout"
-		hasFixedLayout = true
-	case ".cbz", ".cbr", ".cb7", ".cbt":
-		formatGroup = "comic_archive"
-		hasFixedLayout = true
-	default:
-		formatGroup = "unknown"
+		epubIsFixedLayout = fixedErr == nil && isFixed
 	}
+	formatGroup, isReflowable, hasFixedLayout := classifyFormatGroup(ext, epubIsFixedLayout)
 	err = s.db.UpdateMediaItemFormatGroup(ctx, database.UpdateMediaItemFormatGroupParams{
 		ID:              createdItem.ID,
 		FormatGroup:     formatGroup,
@@ -3880,6 +3862,28 @@ func (s *MediaScanner) detectFormatType(filePath string) string {
 	}
 }
 
+// classifyFormatGroup maps a lowercased file extension to the format
+// group and layout flags stored on the media item. `.epub` is passed in
+// with its detected fixed-layout flag because that check needs the file
+// itself.
+func classifyFormatGroup(ext string, epubIsFixedLayout bool) (formatGroup string, isReflowable, hasFixedLayout bool) {
+	switch ext {
+	case ".epub":
+		if epubIsFixedLayout {
+			return "fixed_layout", false, true
+		}
+		return "reflowable", true, false
+	case ".mobi", ".azw", ".azw3", ".fb2", ".txt", ".docx":
+		return "reflowable", true, false
+	case ".pdf", ".djvu":
+		return "fixed_layout", false, true
+	case ".cbz", ".cbr", ".cb7", ".cbt":
+		return "comic_archive", false, true
+	default:
+		return "unknown", false, false
+	}
+}
+
 // extractHashInfo calculates hash and extracts OPF identifiers for a file
 func (s *MediaScanner) extractHashInfo(filePath string) (*HashInfo, *FormatInfo, error) {
 	// Calculate SHA-256