fix(tickets): corrige la perte de focus dans l'édition d'un ticket (#17)

Le focus-trap de FloatingWindow avait un useEffect dépendant de `[onClose]`.
`onClose` (ex. TicketDetail.requestClose) est une closure recréée à chaque
render : chaque frappe ré-armait l'effet et renvoyait le focus au premier
élément focusable, ne laissant saisir qu'une lettre à la fois dans le
formulaire d'édition.

Correctif : conserver le dernier `onClose` dans un `onCloseRef` et passer
l'effet focus-trap en mount-only (`[]`). Le handler Escape lit la valeur
courante via la ref. Ajout d'un test de régression prouvé rouge-sans /
vert-avec le fix.

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

frontend/src/shared/ui/FloatingWindow.test.tsx

@@ -128,6 +128,39 @@ describe("FloatingWindow (#16, G1)", () => {
     expect(onClose).not.toHaveBeenCalled();
   });
 
+  it("keeps focus on a controlled input across renders that change onClose identity (#17 focus-loss bug)", () => {
+    // Reproduces the reported bug: a caller re-creates its `onClose` closure on
+    // every render (as TicketDetail's `requestClose` does). If the focus-trap
+    // effect re-ran on that identity change, focus would jump back to the first
+    // focusable after each keystroke — only one character could be typed.
+    function Harness() {
+      const [value, setValue] = useState("");
+      // New closure identity on every render, like an inline/rebuilt handler.
+      const onClose = () => {};
+      return (
+        <FloatingWindow open title="Panel" onClose={onClose}>
+          <input
+            aria-label="field"
+            value={value}
+            onChange={(e) => setValue(e.target.value)}
+          />
+        </FloatingWindow>
+      );
+    }
+    render(<Harness />);
+    const field = screen.getByRole("textbox", { name: "field" });
+    field.focus();
+    expect(document.activeElement).toBe(field);
+
+    fireEvent.change(field, { target: { value: "a" } });
+    expect(document.activeElement).toBe(field);
+    fireEvent.change(field, { target: { value: "ab" } });
+    fireEvent.change(field, { target: { value: "abc" } });
+    // Focus never left the field, so multi-character input works.
+    expect(document.activeElement).toBe(field);
+    expect((field as HTMLInputElement).value).toBe("abc");
+  });
+
   it("restores focus to the opener when closed", () => {
     function Harness() {
       const [open, setOpen] = useState(false);

frontend/src/shared/ui/FloatingWindow.tsx

@@ -80,6 +80,15 @@ function FloatingWindowBody({
 }: Omit<FloatingWindowProps, "open">) {
   const dialogRef = useRef<HTMLDivElement>(null);
 
+  // Keep the latest `onClose` in a ref so the mount-only effect below never
+  // re-runs when the caller passes an unstable `onClose` closure (a new
+  // identity on each parent render). Re-running the effect would move focus
+  // back to the first focusable element on every keystroke, so a controlled
+  // input inside the window could only accept one character before losing
+  // focus. The Escape handler reads the current value via this ref.
+  const onCloseRef = useRef(onClose);
+  onCloseRef.current = onClose;
+
   useEffect(() => {
     const previouslyFocused = document.activeElement as HTMLElement | null;
     const node = dialogRef.current;
@@ -96,7 +105,7 @@ function FloatingWindowBody({
       if (!isTopmost()) return;
       if (e.key === "Escape") {
         e.preventDefault();
-        onClose();
+        onCloseRef.current();
         return;
       }
       if (e.key !== "Tab" || !node) return;
@@ -128,7 +137,10 @@ function FloatingWindowBody({
       if (i >= 0) windowStack.splice(i, 1);
       previouslyFocused?.focus?.();
     };
-  }, [onClose]);
+    // Mount-only: focus save/restore and listener wiring must not re-run when
+    // `onClose` changes identity (see `onCloseRef` above).
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []);
 
   return (
     <div