feat(templates): add types for progress, unlinked books, and shelf mappings

Add template data types for Phase 9 frontend features:
- ProgressItemData: For reading progress visualization with sync source
- UnlinkedBookData: For unmatched books requiring manual linking
- PotentialMatchData: For book matching suggestions
- DeviceShelfMappingData: For collection-to-shelf mappings

Also adds Theme field to User type for theme support.

templates/types.go

@@ -5,6 +5,7 @@ type User struct {
 	Username string
 	Email    string
 	Role     string
+	Theme    string
 }
 
 type PageData struct {
@@ -76,3 +77,49 @@ type QueueItemData struct {
 	Attempts   int32
 	CreatedAt  string
 }
+
+type DeviceShelfMappingData struct {
+	ID              string
+	CollectionID    string
+	CollectionName  string
+	DeviceShelfName string
+	SyncDirection   string
+	CreatedAt       string
+}
+
+type ProgressItemData struct {
+	MediaItemID        string
+	Title              string
+	Author             string
+	CoverImagePath     string
+	CurrentPage        int32
+	TotalPages         int32
+	ProgressPercentage float64
+	LastUpdated        string
+	DeviceName         string
+	DeviceType         string
+	DeviceIcon         string
+	EpubCFI            string
+}
+
+type UnlinkedBookData struct {
+	ProgressID       string
+	DeviceID         string
+	DeviceType       string
+	DeviceName       string
+	FilePath         string
+	SHA256           string
+	TitleFromDevice  string
+	LastSyncTime     string
+	ConfidenceScore  float64
+	PotentialMatches []PotentialMatchData
+}
+
+type PotentialMatchData struct {
+	MediaItemID    string
+	Title          string
+	Author         string
+	CoverImagePath string
+	MatchMethod    string
+	Confidence     float64
+}