feat: add Rated At field - #4653 (#4660)

* feat(model): add Rated At field - #4653

Signed-off-by: zacaj <zacaj@zacaj.com>

* fix(ui): ignore empty dates in rating/love tooltips - #4653

* refactor(ui): add isDateSet util function

Signed-off-by: zacaj <zacaj@zacaj.com>

* feat: add tests for isDateSet and rated_at sort mappings

Added comprehensive tests for isDateSet and urlValidate functions in
ui/src/utils/validations.test.js covering falsy values, Go zero date handling,
valid date strings, Date objects, and edge cases.

Added rated_at sort mapping to album, artist, and mediafile repositories,
following the same pattern as starred_at (sorting by rating first, then by
timestamp). This enables proper sorting by rating date in the UI.

---------

Signed-off-by: zacaj <zacaj@zacaj.com>
Co-authored-by: zacaj <zacaj@zacaj.com>
Co-authored-by: Deluan <deluan@navidrome.org>

persistence/sql_annotations.go

@@ -28,6 +28,7 @@ func (r sqlRepository) withAnnotation(query SelectBuilder, idField string) Selec
 			"coalesce(rating, 0) as rating",
 			"starred_at",
 			"play_date",
+			"rated_at",
 		)
 	if conf.Server.AlbumPlayCountMode == consts.AlbumPlayCountModeNormalized && r.tableName == "album" {
 		query = query.Columns(
@@ -77,7 +78,8 @@ func (r sqlRepository) SetStar(starred bool, ids ...string) error {
 }
 
 func (r sqlRepository) SetRating(rating int, itemID string) error {
-	return r.annUpsert(map[string]interface{}{"rating": rating}, itemID)
+	ratedAt := time.Now()
+	return r.annUpsert(map[string]interface{}{"rating": rating, "rated_at": ratedAt}, itemID)
 }
 
 func (r sqlRepository) IncPlayCount(itemID string, ts time.Time) error {