refactor: Phase D — composant Modal réutilisable + utilitaire searchParams

- Crée Modal.tsx dans components/ui (backdrop, container, header sticky, close button)
- Remplace le scaffolding modal dupliqué dans EditBookForm, EditSeriesForm,
  DeleteBookButton, MetadataSearchModal (4 composants)
- Crée lib/searchParams.ts avec paramString, paramStringOr, paramInt, paramBool
- Simplifie le parsing des query params dans books, series, authors pages

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/backoffice/app/components/EditBookForm.tsx

@@ -1,7 +1,7 @@
 "use client";
 
 import { useState, useTransition, useEffect, useCallback } from "react";
-import { createPortal } from "react-dom";
+import { Modal } from "./ui/Modal";
 import { useRouter } from "next/navigation";
 import { BookDto } from "@/lib/api";
 import { FormField, FormLabel, FormInput } from "./ui/Form";
@@ -153,34 +153,9 @@ export function EditBookForm({ book }: EditBookFormProps) {
     });
   };
 
-  const modal = isOpen ? createPortal(
-    <>
-      {/* Backdrop */}
-      <div
-        className="fixed inset-0 bg-black/30 backdrop-blur-sm z-50"
-        onClick={() => !isPending && handleClose()}
-      />
-
-      {/* Modal */}
-      <div className="fixed inset-0 flex items-center justify-center z-50 p-4">
-        <div className="bg-card border border-border/50 rounded-xl shadow-2xl w-full max-w-2xl max-h-[90vh] overflow-y-auto animate-in fade-in zoom-in-95 duration-200">
-          {/* Header */}
-          <div className="flex items-center justify-between px-5 py-4 border-b border-border/50 bg-muted/30 sticky top-0 z-10">
-            <h3 className="font-semibold text-foreground">{t("editBook.editMetadata")}</h3>
-            <button
-              type="button"
-              onClick={handleClose}
-              disabled={isPending}
-              className="text-muted-foreground hover:text-foreground transition-colors p-1 hover:bg-accent rounded"
-            >
-              <svg className="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-                <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M6 18L18 6M6 6l12 12" />
-              </svg>
-            </button>
-          </div>
-
-          {/* Body */}
-          <form onSubmit={handleSubmit} className="p-5 space-y-5">
+  const modal = (
+    <Modal isOpen={isOpen} onClose={handleClose} title={t("editBook.editMetadata")} disableClose={isPending}>
+      <form onSubmit={handleSubmit} className="p-5 space-y-5">
             <div className="grid grid-cols-1 sm:grid-cols-2 gap-3">
               <FormField className="sm:col-span-2">
                 <div className="flex items-center gap-1">
@@ -361,11 +336,8 @@ export function EditBookForm({ book }: EditBookFormProps) {
               </button>
             </div>
           </form>
-        </div>
-      </div>
-    </>,
-    document.body
-  ) : null;
+    </Modal>
+  );
 
   return (
     <>