fix(17-02): handle float64 numeric values from Wails JSON deserialization

Wails deserializes JSON numbers from JavaScript as float64, not int.
All .(int) type assertions on year, track_number, and disc_number
silently failed. Add asInt() helper, replace all assertions.

backend/tagwriter/dbsync.go

@@ -117,7 +117,7 @@ func syncDatabase(
 
 		// Determine year value.
 		yearVal := params.oldRecording.Year
-		if yv, yOK := params.changes[FieldYear].(int); yOK {
+		if yv, yOK := asInt(params.changes[FieldYear]); yOK {
 			yearVal = toNullInt64(yv)
 		}
 
@@ -147,12 +147,12 @@ func syncDatabase(
 
 		// Determine track/disc numbers.
 		trackNum := params.oldRecording.TrackNumber
-		if tn, tnOK := params.changes[FieldTrackNumber].(int); tnOK {
+		if tn, tnOK := asInt(params.changes[FieldTrackNumber]); tnOK {
 			trackNum = toNullInt64(tn)
 		}
 
 		discNum := params.oldRecording.DiscNumber
-		if dn, dnOK := params.changes[FieldDiscNumber].(int); dnOK {
+		if dn, dnOK := asInt(params.changes[FieldDiscNumber]); dnOK {
 			discNum = toNullInt64(dn)
 		}
 
@@ -216,17 +216,17 @@ func syncDatabase(
 	}
 
 	newYear := rec.Year
-	if v, ok := params.changes[FieldYear].(int); ok {
+	if v, ok := asInt(params.changes[FieldYear]); ok {
 		newYear = toNullInt64(v)
 	}
 
 	newTrackNum := rec.TrackNumber
-	if v, ok := params.changes[FieldTrackNumber].(int); ok {
+	if v, ok := asInt(params.changes[FieldTrackNumber]); ok {
 		newTrackNum = toNullInt64(v)
 	}
 
 	newDiscNum := rec.DiscNumber
-	if v, ok := params.changes[FieldDiscNumber].(int); ok {
+	if v, ok := asInt(params.changes[FieldDiscNumber]); ok {
 		newDiscNum = toNullInt64(v)
 	}
 

backend/tagwriter/flac.go

@@ -111,10 +111,21 @@ func applyFlacTextChanges(cmt *flacvorbis.MetaDataBlockVorbisComment, changes Ta
 		}
 
 		var val string
+
 		if m.isInt {
-			val = strconv.Itoa(v.(int))
+			n, ok := asInt(v)
+			if !ok {
+				continue
+			}
+
+			val = strconv.Itoa(n)
 		} else {
-			val = v.(string)
+			s, ok := v.(string)
+			if !ok {
+				continue
+			}
+
+			val = s
 		}
 
 		replaceVorbisComment(cmt, m.vorbisID, val)

backend/tagwriter/mp3.go

@@ -62,17 +62,17 @@ func applyTextChanges(tag *id3v2.Tag, changes TagChanges) {
 		tag.SetGenre(v)
 	}
 
-	if v, ok := changes[FieldYear].(int); ok {
+	if v, ok := asInt(changes[FieldYear]); ok {
 		tag.SetYear(strconv.Itoa(v))
 	}
 
-	if v, ok := changes[FieldTrackNumber].(int); ok {
+	if v, ok := asInt(changes[FieldTrackNumber]); ok {
 		trckID := tag.CommonID("Track number/Position in set")
 		tag.DeleteFrames(trckID)
 		tag.AddTextFrame(trckID, id3v2.EncodingUTF8, strconv.Itoa(v))
 	}
 
-	if v, ok := changes[FieldDiscNumber].(int); ok {
+	if v, ok := asInt(changes[FieldDiscNumber]); ok {
 		tposID := tag.CommonID("Part of a set")
 		tag.DeleteFrames(tposID)
 		tag.AddTextFrame(tposID, id3v2.EncodingUTF8, strconv.Itoa(v))

backend/tagwriter/tagwriter.go

@@ -55,6 +55,24 @@ func DetectFormat(filePath string) (AudioFormat, error) {
 	}
 }
 
+// asInt extracts an integer from a TagChanges value.  JSON numbers from
+// Wails arrive as float64; Go callers may pass int.  Returns (value, true)
+// on success or (0, false) if the value is not a recognised numeric type.
+func asInt(v any) (int, bool) {
+	switch n := v.(type) {
+	case int:
+		return n, true
+	case float64:
+		return int(n), true
+	case int64:
+		return int(n), true
+	case float32:
+		return int(n), true
+	default:
+		return 0, false
+	}
+}
+
 // detectMIME returns the MIME type of image data by checking magic bytes.
 func detectMIME(data []byte) string {
 	if len(data) >= 2 && data[0] == 0xFF && data[1] == 0xD8 {