feat(backend): add EPUB CFI and percentage to reading progress

Enhance reading progress tracking to support EPUB-specific location data:
- Add epubcfi field to store EPUB Canonical Fragment Identifier
- Add percentage field for normalized position across formats
- Update UpdateReadingProgress API handler to accept new fields
- Modify database queries to persist additional progress metadata

This enables precise position tracking in reflowable EPUB content
where page numbers are insufficient for accurate bookmarking.

internal/database/queries.sql.go

@@ -9579,6 +9579,8 @@ type UpdateReadingProgressParams struct {
 	UserID      pgtype.UUID `db:"user_id" json:"user_id"`
 	CurrentPage pgtype.Int4 `db:"current_page" json:"current_page"`
 	TotalPages  pgtype.Int4 `db:"total_pages" json:"total_pages"`
+	Epubcfi     string      `json:"epubcfi"`
+	Percentage  float64     `json:"percentage"`
 }
 
 func (q *Queries) UpdateReadingProgress(ctx context.Context, arg UpdateReadingProgressParams) (ReadingProgress, error) {

internal/handlers/media.go

@@ -921,8 +921,10 @@ func (mh *MediaHandler) UpdateMediaReadingProgress(c *echo.Context) error {
 	}
 
 	var req struct {
-		CurrentPage int32 `json:"current_page"`
-		TotalPages  int32 `json:"total_pages"`
+		CurrentPage int32   `json:"current_page"`
+		TotalPages  int32   `json:"total_pages"`
+		Epubcfi     string  `json:"epubcfi"`
+		Percentage  float64 `json:"percentage"`
 	}
 	if err := c.Bind(&req); err != nil {
 		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid request"})
@@ -936,6 +938,8 @@ func (mh *MediaHandler) UpdateMediaReadingProgress(c *echo.Context) error {
 		UserID:      pgtype.UUID{Bytes: userUUID, Valid: true},
 		CurrentPage: pgtype.Int4{Int32: req.CurrentPage, Valid: true},
 		TotalPages:  pgtype.Int4{Int32: req.TotalPages, Valid: req.TotalPages > 0},
+		Epubcfi:     req.Epubcfi,
+		Percentage:  req.Percentage,
 	})
 	if err != nil {
 		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})