Convert range_slider.js to TypeScript (issue #17)

- Add ts/range_slider.ts: typed port of the custom range-slider widget. Number
  inputs typed as HTMLInputElement; setTargetValue coerces via String(); mouse
  handlers typed MouseEvent; var → const/let
- Point the RangeSlider component Media and every e2e/test reference at the
  compiled dist/range_slider.js

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_rendered_pages.py

@@ -65,7 +65,7 @@ class RenderedPagesTest(TestCase):
         html = self.get("games:list_games").content.decode()
         self.assertIn("js/dist/filter_bar.js", html)
         self.assertIn("js/dist/search_select.js", html)
-        self.assertIn("js/range_slider.js", html)
+        self.assertIn("js/dist/range_slider.js", html)
 
     def test_stats_page_auto_loads_datepicker(self):
         """YearPicker declares the datepicker UMD bundle as media; the stats