Convert onSwap widgets to custom elements (issue #18)

Replaces the four onSwap-based widgets with TypeScript custom elements
following the pattern from PR #16. Each widget gets a class extending
HTMLElement with connectedCallback/disconnectedCallback, typed props via
register_element + gen_element_types codegen, and lives in ts/elements/.

- range-slider: RangeSliderElement; Python uses _RangeSlider builder
- date-range-picker: DateRangePickerElement; Python uses _DateRangePicker builder
- search-select: SearchSelectElement; Python uses _SearchSelect builder;
  data-* attrs become plain attrs (data-name -> name, data-search-url -> search-url, etc.)
- filter-bar: FilterBarElement; props carry preset URLs; onclick/onsubmit
  attrs replaced with data-filter-bar-* sentinel attrs; all window.* globals removed

Deletes ts/range_slider.ts, ts/search_select.ts, ts/date_range_picker.ts,
ts/filter_bar.ts. Updates all tests and e2e pages to use the new element
selectors and script paths (dist/elements/<tag>.js).

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

tests/test_filters.py

@@ -555,8 +555,8 @@ class TestFilterBarRendering:
 
     def test_status_uses_filter_select(self):
         html = str(FilterBar())
-        assert 'data-search-select-mode="filter"' in html
-        assert 'data-name="status"' in html
+        assert 'filter-mode="true"' in html
+        assert 'name="status"' in html
 
     def test_mastered_not_checked_by_default(self):
         html = str(FilterBar(filter_json=""))
@@ -602,13 +602,13 @@ class TestFilterBarRendering:
     def test_platform_uses_search_url(self):
         """Platform is model-backed: rows are fetched, not pre-rendered."""
         html = str(FilterBar())
-        assert 'data-search-url="/api/platforms/search"' in html
+        assert 'search-url="/api/platforms/search"' in html
 
     def test_status_has_no_modifiers(self):
         """Non-nullable fields should not show (None) but MUST show (Any)."""
         html = str(FilterBar())
-        status_start = html.find('data-name="status"')
-        platform_start = html.find('data-name="platform"')
+        status_start = html.find('name="status"')
+        platform_start = html.find('name="platform"')
         status_section = html[status_start:platform_start]
         # Must have (Any) — always available
         assert "(Any)" in status_section
@@ -618,7 +618,7 @@ class TestFilterBarRendering:
     def test_platform_has_modifiers(self):
         """Nullable ForeignKey fields should show (Any)/(None)."""
         html = str(FilterBar())
-        platform_start = html.find('data-name="platform"')
+        platform_start = html.find('name="platform"')
         platform_section = html[platform_start:]
         # Should have at least one modifier option
         assert "(Any)" in platform_section or "(None)" in platform_section