Convert search_select.js to TypeScript (issue #17)

- Add ts/search_select.ts: typed port of the SearchSelect/FilterSelect widget.
  Exports SearchSelectOption / SearchSelectChangeDetail as the single source of
  truth for the "search-select:change" event contract
- add_purchase.ts now imports those types via `import type` (no runtime
  coupling), instead of redefining them locally
- Declare window.readSearchSelect in ts/globals.d.ts
- Point the SearchSelect component Media and every view/e2e/test reference at
  the compiled dist/search_select.js
- Update doc comments in common/components/search_select.py to name the TS source

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

ts/add_purchase.ts

@@ -1,16 +1,5 @@
 import { disableElementsWhenTrue, onSwap } from "./utils.js";
-
-interface SearchSelectOption {
-  value: string;
-  label: string;
-  data: Record<string, string>;
-}
-
-interface SearchSelectChangeDetail {
-  name: string;
-  values: string[];
-  last: SearchSelectOption | null;
-}
+import type { SearchSelectChangeDetail } from "./search_select.js";
 
 // Switch between a single bundle price and one price per game. The per-game
 // inputs are the selection-fields element; this only sets the policy: the