feat(workstate): UI live-state des conversations/délégations (Lot A frontend)

Ajoute le port et l'adaptateur workState (+ mock) côté frontend, le type domaine
associé, et la feature `workstate` (panneau ProjectWorkStatePanel + hook
useProjectWorkState) consommant le read-model live exposé par le backend.
Intègre le panneau dans ProjectsView. Tests verts (workstate + projects).

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

frontend/src/features/workstate/useProjectWorkState.ts

@@ -0,0 +1,73 @@
+/**
+ * View-model hook for the project work-state read-model.
+ *
+ * It consumes the WorkStateGateway only, and optionally subscribes to existing
+ * domain events through SystemGateway to refresh the read-only snapshot.
+ */
+
+import { useCallback, useEffect, useState } from "react";
+
+import type { GatewayError, ProjectWorkState } from "@/domain";
+import { useGateways } from "@/app/di";
+
+export interface ProjectWorkStateViewModel {
+  state: ProjectWorkState | null;
+  error: string | null;
+  busy: boolean;
+  refresh: () => Promise<void>;
+}
+
+function describe(e: unknown): string {
+  if (e && typeof e === "object" && "message" in e) {
+    return String((e as GatewayError).message);
+  }
+  return String(e);
+}
+
+export function useProjectWorkState(projectId: string): ProjectWorkStateViewModel {
+  const { workState, system } = useGateways();
+  const [state, setState] = useState<ProjectWorkState | null>(null);
+  const [error, setError] = useState<string | null>(null);
+  const [busy, setBusy] = useState(false);
+
+  const refresh = useCallback(async () => {
+    setBusy(true);
+    setError(null);
+    try {
+      setState(await workState.getProjectWorkState(projectId));
+    } catch (e) {
+      setError(describe(e));
+    } finally {
+      setBusy(false);
+    }
+  }, [projectId, workState]);
+
+  useEffect(() => {
+    void refresh();
+  }, [refresh]);
+
+  useEffect(() => {
+    if (!system) return;
+    let unsubscribe: (() => void) | undefined;
+    let cancelled = false;
+    void system.onDomainEvent((event) => {
+      if (
+        event.type === "agentLaunched" ||
+        event.type === "agentExited" ||
+        event.type === "agentBusyChanged" ||
+        event.type === "orchestratorRequestProcessed"
+      ) {
+        void refresh();
+      }
+    }).then((u) => {
+      if (cancelled) u();
+      else unsubscribe = u;
+    });
+    return () => {
+      cancelled = true;
+      unsubscribe?.();
+    };
+  }, [refresh, system]);
+
+  return { state, error, busy, refresh };
+}