feat(templates): expand reader and progress template types for format-aware display

Add fields to ReaderMetadata and ReadingProgress template types to support
KOReader-like progress display:

ReaderMetadata:
- TotalCharacters: from media item, used for estimated page calculation
- EstimatedPages: computed via sync.EstimatedPages()

ReadingProgress:
- Chapter: current chapter index from reading_progress
- ChapterProgress: within-chapter progress (0-100, multiplied from DB fraction)
- FormatGroup: item format for conditional display logic

These fields enable format-aware progress display (pages for comics/PDFs,
estimated pages for reflowable, percentage for all).

templates/types.go

@@ -161,17 +161,22 @@ type ReaderMetadata struct {
 	ReadingDirection string `json:"reading_direction"`
 	FileURL          string `json:"file_url"`
 	LibraryID        string `json:"library_id"`
+	TotalCharacters  int64  `json:"total_characters"`
+	EstimatedPages   int    `json:"estimated_pages"`
 }
 
 type ReadingProgress struct {
-	ID          string
-	MediaItemID string
-	UserID      string
-	CurrentPage int
-	TotalPages  int
-	Percentage  float64
-	EpubCfi     string
-	LastReadAt  time.Time
+	ID              string
+	MediaItemID     string
+	UserID          string
+	CurrentPage     int
+	TotalPages      int
+	Percentage      float64
+	EpubCfi         string
+	LastReadAt      time.Time
+	Chapter         int
+	ChapterProgress float64
+	FormatGroup     string
 }
 
 type Bookmark struct {