feat(tickets): multi-sélection dans TicketPicker (#41)

Le TicketPicker permet la sélection multiple de tickets ; SprintManager
consomme la sélection multiple. Frontend-pur.

QA vert : tsc --noEmit exit 0, vitest 62 fichiers / 620 tests passés.

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

frontend/src/features/tickets/TicketPicker.test.tsx

@@ -241,4 +241,108 @@ describe("TicketPicker (#18)", () => {
     expect(onClose).not.toHaveBeenCalled();
     readSpy.mockRestore();
   });
+
+  describe("multi-select (#41)", () => {
+    it("toggles rows without closing and confirms the resolved array", async () => {
+      const [a, , c] = await seedTrio(ticket);
+      const { onSelect, onClose } = renderPicker(ticket, {
+        selectionMode: "multi",
+        confirmLabel: "Ajouter au sprint",
+      });
+
+      await screen.findByText("Alpha bug");
+
+      const confirm = screen.getByLabelText(
+        "confirm ticket selection",
+      ) as HTMLButtonElement;
+      // Empty selection ⇒ confirm disabled, count reads 0.
+      expect(confirm.disabled).toBe(true);
+      expect(screen.getByText("0 sélectionné")).toBeTruthy();
+
+      // Select two rows; the picker stays open and does not fire onSelect yet.
+      fireEvent.click(screen.getByLabelText(`select ticket ${a.ref}`));
+      fireEvent.click(screen.getByLabelText(`select ticket ${c.ref}`));
+      expect(onSelect).not.toHaveBeenCalled();
+      expect(onClose).not.toHaveBeenCalled();
+
+      // Visual state: the toggled rows expose aria-checked.
+      expect(
+        screen.getByLabelText(`select ticket ${a.ref}`).getAttribute("aria-checked"),
+      ).toBe("true");
+      expect(screen.getByText("2 sélectionnés")).toBeTruthy();
+      expect(confirm.textContent).toContain("2");
+      expect(confirm.disabled).toBe(false);
+
+      // Toggle one back off ⇒ count drops, still open.
+      fireEvent.click(screen.getByLabelText(`select ticket ${a.ref}`));
+      expect(screen.getByText("1 sélectionné")).toBeTruthy();
+      expect(
+        screen.getByLabelText(`select ticket ${a.ref}`).getAttribute("aria-checked"),
+      ).toBe("false");
+
+      // Re-select and confirm ⇒ onSelect receives the resolved array, then close.
+      fireEvent.click(screen.getByLabelText(`select ticket ${a.ref}`));
+      fireEvent.click(confirm);
+
+      await waitFor(() => expect(onSelect).toHaveBeenCalledTimes(1));
+      const results = onSelect.mock.calls[0][0] as TicketPickerResult[];
+      expect(Array.isArray(results)).toBe(true);
+      expect(results.map((r) => r.ref).sort()).toEqual([a.ref, c.ref].sort());
+      expect(results).toContainEqual(
+        expect.objectContaining({ ref: a.ref, id: a.id, number: a.number }),
+      );
+      expect(onClose).toHaveBeenCalledTimes(1);
+    });
+
+    it("confirm stays disabled when selection is empty", async () => {
+      await seedTrio(ticket);
+      const { onSelect } = renderPicker(ticket, { selectionMode: "multi" });
+      await screen.findByText("Alpha bug");
+
+      const confirm = screen.getByLabelText(
+        "confirm ticket selection",
+      ) as HTMLButtonElement;
+      expect(confirm.disabled).toBe(true);
+      // Clicking a disabled button is a no-op.
+      fireEvent.click(confirm);
+      expect(onSelect).not.toHaveBeenCalled();
+    });
+
+    it("respects excludeRefs and facet filters in multi mode", async () => {
+      const [a, b] = await seedTrio(ticket);
+      renderPicker(ticket, {
+        selectionMode: "multi",
+        excludeRefs: [a.ref],
+      });
+
+      // Excluded ref is not selectable.
+      await screen.findByText("Bravo task");
+      expect(screen.queryByLabelText(`select ticket ${a.ref}`)).toBeNull();
+      expect(screen.getByLabelText(`select ticket ${b.ref}`)).toBeTruthy();
+
+      // Facets still narrow the list (Open ⇒ only Alpha, which is excluded ⇒ none).
+      fireEvent.click(screen.getByLabelText("filter status Open"));
+      await waitFor(() =>
+        expect(screen.getByText("No matching tickets.")).toBeTruthy(),
+      );
+    });
+
+    it("closes on Escape and backdrop without confirming", async () => {
+      const [a] = await seedTrio(ticket);
+      const { onSelect, onClose } = renderPicker(ticket, {
+        selectionMode: "multi",
+      });
+      await screen.findByText("Alpha bug");
+      fireEvent.click(screen.getByLabelText(`select ticket ${a.ref}`));
+
+      fireEvent.keyDown(document, { key: "Escape" });
+      expect(onClose).toHaveBeenCalledTimes(1);
+      expect(onSelect).not.toHaveBeenCalled();
+
+      const backdrop = screen.getByRole("dialog").parentElement as HTMLElement;
+      fireEvent.mouseDown(backdrop);
+      expect(onClose).toHaveBeenCalledTimes(2);
+      expect(onSelect).not.toHaveBeenCalled();
+    });
+  });
 });