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>

e2e/test_widgets_e2e.py

@@ -31,7 +31,7 @@ def open_filter_bar(page: Page) -> None:
 
 
 def status_filter_widget(page: Page):
-    return page.locator('[data-search-select][data-name="status"]')
+    return page.locator('search-select[name="status"]')
 
 
 def test_search_select_initializes_on_page_load(authenticated_page: Page, live_server):
@@ -78,12 +78,11 @@ def test_range_slider_mode_toggle_fires_exactly_once(
     page.goto(f"{live_server.url}{reverse('games:list_games')}")
     open_filter_bar(page)
 
-    block = page.locator(".range-slider-block").first
-    slider = block.locator(".range-slider")
-    expect(slider).to_have_attribute("data-mode", "range")
+    slider = page.locator("range-slider").first
+    expect(slider).to_have_attribute("mode", "range")
 
-    block.locator(".range-mode-toggle").click()
-    expect(slider).to_have_attribute("data-mode", "point")
+    slider.locator(".range-mode-toggle").click()
+    expect(slider).to_have_attribute("mode", "point")
 
 
 def test_widgets_initialize_inside_htmx_swapped_content(
@@ -110,11 +109,10 @@ def test_widgets_initialize_inside_htmx_swapped_content(
     widget.locator("[data-search-select-search]").click()
     expect(widget.locator("[data-search-select-options]")).to_be_visible()
 
-    block = page.locator(".range-slider-block").first
-    slider = block.locator(".range-slider")
-    expect(slider).to_have_attribute("data-mode", "range")
-    block.locator(".range-mode-toggle").click()
-    expect(slider).to_have_attribute("data-mode", "point")
+    slider = page.locator("range-slider").first
+    expect(slider).to_have_attribute("mode", "range")
+    slider.locator(".range-mode-toggle").click()
+    expect(slider).to_have_attribute("mode", "point")
 
 
 def test_add_purchase_type_toggles_disabled_fields(
@@ -149,9 +147,9 @@ def test_add_purchase_related_game_is_flat_game_search(
     page = authenticated_page
     page.goto(f"{live_server.url}{reverse('games:add_purchase')}")
 
-    related = page.locator('[data-search-select][data-name="related_game"]')
+    related = page.locator('search-select[name="related_game"]')
     expect(related).to_have_count(1)
-    expect(related).to_have_attribute("data-search-url", "/api/games/search")
+    expect(related).to_have_attribute("search-url", "/api/games/search")
 
 
 def test_searchselect_border_matches_native_input(