feat(tickets): persistance des filtres tickets entre redémarrages (#29)

Introduit le port UiPreferencesGateway et son adapter uiPreferences,
avec le module ticketFilterPersistence qui sauvegarde/restaure les
filtres (recherche, statut, sprint, agents) via useTickets,
useTicketSearch et useProjectAgents. Couvert par tests unitaires et
un test d'intégration.

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

frontend/src/ports/index.ts

@@ -971,6 +971,29 @@ export interface WindowGateway {
   ): Promise<Unsubscribe>;
 }
 
+/**
+ * Thin UI-preferences port (ticket #29). Persists small, per-surface pieces of
+ * UI state (like the ticket filters) so they survive a restart / reopen. This is
+ * **frontend-owned** state: the backend stays the source of tickets, never of UI
+ * preferences. Values are opaque JSON blobs addressed by an explicit string key;
+ * the adapter serialises/parses them. Reads are best-effort — an absent or
+ * corrupt entry yields `null` so callers fall back to their default state, and
+ * writes never throw (a full/blocked store degrades to "not persisted").
+ *
+ * Deliberately synchronous: hydration happens during a component's first render,
+ * so the persisted state is applied without a flash of default filters. The
+ * localStorage adapter is synchronous; a future async backend (Tauri store)
+ * would front this with an in-memory cache to keep the contract.
+ */
+export interface UiPreferencesGateway {
+  /** Reads and JSON-parses the blob at `key`; `null` when absent or invalid. */
+  read(key: string): unknown;
+  /** JSON-serialises and persists `value` at `key`. Best-effort (never throws). */
+  write(key: string, value: unknown): void;
+  /** Removes any persisted blob at `key`. Best-effort (never throws). */
+  remove(key: string): void;
+}
+
 /**
  * The full set of gateways the app depends on, injected via the DI provider.
  * The composition (real vs mock) is chosen in `app/`.
@@ -995,4 +1018,5 @@ export interface Gateways {
   conversation: ConversationGateway;
   ticket: TicketGateway;
   window: WindowGateway;
+  uiPreferences: UiPreferencesGateway;
 }