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>

games/views/session.py

@@ -249,7 +249,7 @@ def add_session(request: HttpRequest, game_id: int = 0) -> HttpResponse:
         request,
         AddForm(form, request=request, fields=_session_fields(form), submit_class=""),
         title="Add New Session",
-        scripts=mark_safe(ModuleScript("dist/search_select.js")),
+        scripts=mark_safe(ModuleScript("dist/elements/search-select.js")),
     )
 
 
@@ -264,7 +264,7 @@ def edit_session(request: HttpRequest, session_id: int) -> HttpResponse:
         request,
         AddForm(form, request=request, fields=_session_fields(form), submit_class=""),
         title="Edit Session",
-        scripts=mark_safe(ModuleScript("dist/search_select.js")),
+        scripts=mark_safe(ModuleScript("dist/elements/search-select.js")),
     )