feat(tickets): popup réutilisable de sélection de ticket (#18)

Ajoute TicketPicker, popup modale réutilisable de sélection de ticket,
socle du chemin critique du sprint UI rework (#17 et #19 en dépendent).

- TicketPicker.tsx : popup de recherche/sélection réutilisable
- useTicketSearch.ts : hook de recherche/filtrage extrait et partagé
- TicketFacetsBar.tsx : barre de facettes extraite de TicketsPanel
  pour réutilisation (listing principal + picker)
- shared/ui/zIndex.ts : échelle z-index centralisée
- TicketsPanel : consomme la barre de facettes extraite

Tests : TicketPicker.test.tsx 8/8, suite tickets 37/37, tsc --noEmit clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/features/tickets/index.ts

@@ -9,6 +9,19 @@ export { TicketDetail } from "./TicketDetail";
 export type { TicketDetailProps } from "./TicketDetail";
 export { SprintManager } from "./SprintManager";
 export type { SprintManagerProps } from "./SprintManager";
+export { TicketPicker } from "./TicketPicker";
+export type {
+  TicketPickerProps,
+  TicketPickerResult,
+  TicketPickerSelectionMode,
+} from "./TicketPicker";
+export { TicketFacetsBar } from "./TicketFacetsBar";
+export type { TicketFacetsBarProps } from "./TicketFacetsBar";
+export { useTicketSearch } from "./useTicketSearch";
+export type {
+  TicketSearchViewModel,
+  UseTicketSearchOptions,
+} from "./useTicketSearch";
 export { useTickets } from "./useTickets";
 export type { TicketsViewModel } from "./useTickets";
 export { useTicketDetail } from "./useTicketDetail";