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>

ui/src/common/RatingField.jsx

@@ -2,6 +2,7 @@ import React, { useCallback } from 'react'
 import PropTypes from 'prop-types'
 import Rating from '@material-ui/lab/Rating'
 import { makeStyles } from '@material-ui/core/styles'
+import { isDateSet } from '../utils/validations'
 import StarBorderIcon from '@material-ui/icons/StarBorder'
 import clsx from 'clsx'
 import { useRating } from './useRating'
@@ -45,7 +46,14 @@ export const RatingField = ({
   )
 
   return (
-    <span onClick={(e) => stopPropagation(e)}>
+    <span
+      onClick={(e) => stopPropagation(e)}
+      title={
+        isDateSet(record.ratedAt)
+          ? new Date(record.ratedAt).toLocaleString()
+          : undefined
+      }
+    >
       <Rating
         name={record.mediaFileId || record.id}
         className={clsx(