fix(reader): scale percentage correctly, add 5s init guard

- reader.templ: divide DB percentage (0-1) by 100 was wrong; actually
  the router multiplies by 100, so template now divides by 100 to get
  back to 0-1 range for foliate-js savedPercentage
- reader.ts: add 5-second initTime guard to prevent overwriting
  existing progress with initial position on page load

templates/reader.templ

@@ -14,7 +14,7 @@ func readerInitExpr(metadata ReaderMetadata, progress ReadingProgress) string {
 		"mangaType":        metadata.MangaType,
 	}
 	if progress.Percentage > 0 {
-		config["savedPercentage"] = progress.Percentage
+		config["savedPercentage"] = progress.Percentage / 100
 	}
 	if progress.EpubCfi != "" {
 		config["savedCfi"] = progress.EpubCfi

templates/reader_templ.go

@@ -22,7 +22,7 @@ func readerInitExpr(metadata ReaderMetadata, progress ReadingProgress) string {
 		"mangaType":        metadata.MangaType,
 	}
 	if progress.Percentage > 0 {
-		config["savedPercentage"] = progress.Percentage
+		config["savedPercentage"] = progress.Percentage / 100
 	}
 	if progress.EpubCfi != "" {
 		config["savedCfi"] = progress.EpubCfi