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>

model/criteria/fields.go

@@ -44,6 +44,7 @@ var fieldMap = map[string]*mappedField{
 	"loved":                {field: "COALESCE(annotation.starred, false)"},
 	"dateloved":            {field: "annotation.starred_at"},
 	"lastplayed":           {field: "annotation.play_date"},
+	"daterated":            {field: "annotation.rated_at"},
 	"playcount":            {field: "COALESCE(annotation.play_count, 0)"},
 	"rating":               {field: "COALESCE(annotation.rating, 0)"},
 	"mbz_album_id":         {field: "media_file.mbz_album_id"},