feat(frontend): système de plugins — runtime, menus, layouts custom (#43)

Lots F1-F4 : runtime de chargement/registre plugin, extension des menus
existants, panneau de gestion des plugins, types de layout custom
(sélecteur, fallback, cellule dédiée) branchés sur le port plugin.
Suite npm typecheck/test verte (947/947).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/features/plugins/PluginConfirmDialog.tsx

@@ -0,0 +1,76 @@
+/**
+ * A small modal confirmation, local to the plugins feature (ticket #43, F2).
+ * Mirrors `features/devices/ConfirmDialog` (not shared — that dialog is itself
+ * feature-local by design, see its header comment); duplicated rather than
+ * cross-imported to keep each feature's public surface to its own `index.ts`.
+ */
+
+import { useEffect, useRef } from "react";
+
+import { Button, zIndex } from "@/shared";
+
+interface PluginConfirmDialogProps {
+  title: string;
+  body: string;
+  confirmLabel: string;
+  danger?: boolean;
+  busy?: boolean;
+  onConfirm: () => void | Promise<void>;
+  onCancel: () => void;
+}
+
+export function PluginConfirmDialog({
+  title,
+  body,
+  confirmLabel,
+  danger = false,
+  busy = false,
+  onConfirm,
+  onCancel,
+}: PluginConfirmDialogProps) {
+  const cancelRef = useRef<HTMLButtonElement>(null);
+
+  useEffect(() => {
+    cancelRef.current?.focus();
+  }, []);
+
+  useEffect(() => {
+    function onKeyDown(e: KeyboardEvent) {
+      if (e.key === "Escape") onCancel();
+    }
+    window.addEventListener("keydown", onKeyDown);
+    return () => window.removeEventListener("keydown", onKeyDown);
+  }, [onCancel]);
+
+  return (
+    <div
+      className="fixed inset-0 flex items-center justify-center bg-black/50 p-4"
+      style={{ zIndex: zIndex.floatingWindow }}
+      onClick={onCancel}
+    >
+      <div
+        role="dialog"
+        aria-modal="true"
+        aria-label={title}
+        onClick={(e) => e.stopPropagation()}
+        className="flex w-full max-w-md flex-col gap-3 rounded-lg border border-border bg-raised p-4 shadow-xl"
+      >
+        <h3 className="text-sm font-semibold text-content">{title}</h3>
+        <p className="whitespace-pre-line text-sm text-muted">{body}</p>
+        <div className="flex justify-end gap-2">
+          <Button ref={cancelRef} size="sm" variant="ghost" onClick={onCancel}>
+            Annuler
+          </Button>
+          <Button
+            size="sm"
+            variant={danger ? "danger" : "primary"}
+            loading={busy}
+            onClick={() => void onConfirm()}
+          >
+            {confirmLabel}
+          </Button>
+        </div>
+      </div>
+    </div>
+  );
+}