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/utils/validations.test.js

@@ -0,0 +1,73 @@
+import { isDateSet, urlValidate } from './validations'
+
+describe('urlValidate', () => {
+  it('returns undefined for valid URLs', () => {
+    expect(urlValidate('https://example.com')).toBeUndefined()
+    expect(urlValidate('http://localhost:3000')).toBeUndefined()
+    expect(urlValidate('ftp://files.example.com')).toBeUndefined()
+  })
+
+  it('returns undefined for empty values', () => {
+    expect(urlValidate('')).toBeUndefined()
+    expect(urlValidate(null)).toBeUndefined()
+    expect(urlValidate(undefined)).toBeUndefined()
+  })
+
+  it('returns error for invalid URLs', () => {
+    expect(urlValidate('not-a-url')).toEqual('ra.validation.url')
+    expect(urlValidate('example.com')).toEqual('ra.validation.url')
+    expect(urlValidate('://missing-protocol')).toEqual('ra.validation.url')
+  })
+})
+
+describe('isDateSet', () => {
+  describe('with falsy values', () => {
+    it('returns false for null', () => {
+      expect(isDateSet(null)).toBe(false)
+    })
+
+    it('returns false for undefined', () => {
+      expect(isDateSet(undefined)).toBe(false)
+    })
+
+    it('returns false for empty string', () => {
+      expect(isDateSet('')).toBe(false)
+    })
+  })
+
+  describe('with Go zero date string', () => {
+    it('returns false for Go zero date', () => {
+      expect(isDateSet('0001-01-01T00:00:00Z')).toBe(false)
+    })
+  })
+
+  describe('with valid date strings', () => {
+    it('returns true for ISO date strings', () => {
+      expect(isDateSet('2024-01-15T10:30:00Z')).toBe(true)
+      expect(isDateSet('2023-12-25T00:00:00Z')).toBe(true)
+    })
+
+    it('returns true for other date formats', () => {
+      expect(isDateSet('2024-01-15')).toBe(true)
+    })
+  })
+
+  describe('with Date objects', () => {
+    it('returns true for valid Date objects', () => {
+      expect(isDateSet(new Date())).toBe(true)
+      expect(isDateSet(new Date('2024-01-15T10:30:00Z'))).toBe(true)
+    })
+
+    // Note: Date objects representing Go zero date would return true because
+    // toISOString() adds milliseconds (0001-01-01T00:00:00.000Z).
+    // In practice, dates from the API come as strings, not Date objects,
+    // so this edge case doesn't occur.
+  })
+
+  describe('with other truthy values', () => {
+    it('returns true for non-date truthy values', () => {
+      expect(isDateSet(123)).toBe(true)
+      expect(isDateSet({})).toBe(true)
+    })
+  })
+})