feat(tickets): suppression d'un ticket (backend + frontend)

Ajoute la suppression complète d'un ticket (#6).

Backend Rust :
- port IssueStore::delete (NotFound si absent) + event IssueDeleted{freed_sprint}
- FsIssueStore::delete : supprime .ideai/tickets/<N>/ et l'index sous lock
- use case DeleteIssue + adaptations des tests sprint/ticket_assistant au port
- commande Tauri ticket_delete + câblage events/state/lib

Frontend :
- gateway delete (ports, adapter ticket + mock, domain)
- useTicketDetail : retrait de la liste et fermeture du détail via event issueDeleted
- intégration TicketDetail + tests

Tests verts : application/issue_usecases (6), infrastructure/issue_store (7),
app-tauri --lib (56), frontend vitest (503), npm run build (exit 0).

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

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

@@ -14,7 +14,7 @@ import {
   MockSystemGateway,
   MockTicketGateway,
 } from "@/adapters/mock";
-import type { Agent } from "@/domain";
+import type { Agent, DomainEvent } from "@/domain";
 import type { Gateways } from "@/ports";
 import { TicketsView } from "./TicketsView";
 import { TicketDetail } from "./TicketDetail";
@@ -108,6 +108,34 @@ describe("MockTicketGateway", () => {
     ).rejects.toMatchObject({ message: expect.stringContaining("version conflict") });
   });
 
+  it("deletes a ticket, removing it and emitting issueDeleted with freedSprint (#6)", async () => {
+    ticket._seedSprint(PROJECT_ID, { id: "s1", order: 1, name: "S" });
+    const t = await ticket.create(PROJECT_ID, { title: "Doomed" });
+    await ticket.setTicketSprint(PROJECT_ID, t.ref, "s1", t.version);
+    const events: DomainEvent[] = [];
+    await system.onDomainEvent((e) => events.push(e));
+
+    await ticket.delete(PROJECT_ID, t.ref);
+
+    // Removed from the store (NotFound afterwards)…
+    await expect(ticket.read(PROJECT_ID, t.ref)).rejects.toMatchObject({
+      code: "NOT_FOUND",
+    });
+    // …and the sprint it was released from is reported on the event.
+    expect(events).toContainEqual({
+      type: "issueDeleted",
+      projectId: PROJECT_ID,
+      issueRef: t.ref,
+      freedSprint: "s1",
+    });
+  });
+
+  it("rejects deleting an unknown ticket with NotFound (#6)", async () => {
+    await expect(ticket.delete(PROJECT_ID, "#404")).rejects.toMatchObject({
+      code: "NOT_FOUND",
+    });
+  });
+
   it("links and unlinks tickets, bumping the version", async () => {
     const a = await ticket.create(PROJECT_ID, { title: "a" });
     await ticket.create(PROJECT_ID, { title: "b" });
@@ -425,6 +453,69 @@ describe("TicketsView", () => {
     ).toBeNull();
   });
 
+  it("deletes a ticket from the detail: confirmation ⇒ row gone + detail closed (#6)", async () => {
+    const t = await ticket.create(PROJECT_ID, { title: "Deletable" });
+    renderView(ticket, system, agent);
+
+    fireEvent.click(await screen.findByText("Deletable"));
+    const detail = await screen.findByRole("dialog", {
+      name: `ticket ${t.ref}`,
+    });
+
+    // Open the confirmation, then confirm the deletion.
+    fireEvent.click(within(detail).getByText("Supprimer"));
+    const confirm = await screen.findByRole("dialog", {
+      name: "confirmer la suppression",
+    });
+    fireEvent.click(within(confirm).getByLabelText("confirm delete"));
+
+    // The gateway removed the ticket…
+    await waitFor(() =>
+      expect(ticket.read(PROJECT_ID, t.ref)).rejects.toMatchObject({
+        code: "NOT_FOUND",
+      }),
+    );
+    // …the detail closed (via the `issueDeleted` event → `deleted` flag)…
+    await waitFor(() =>
+      expect(
+        screen.queryByRole("dialog", { name: `ticket ${t.ref}` }),
+      ).toBeNull(),
+    );
+    // …and the row disappeared from the list (event-driven refresh).
+    await waitFor(() => expect(screen.queryByText("Deletable")).toBeNull());
+    expect(await screen.findByText("No tickets.")).toBeTruthy();
+  });
+
+  it("cancelling the delete confirmation keeps the ticket (#6)", async () => {
+    const t = await ticket.create(PROJECT_ID, { title: "Keeper" });
+    const delSpy = vi.spyOn(ticket, "delete");
+    renderView(ticket, system, agent);
+
+    fireEvent.click(await screen.findByText("Keeper"));
+    const detail = await screen.findByRole("dialog", {
+      name: `ticket ${t.ref}`,
+    });
+
+    fireEvent.click(within(detail).getByText("Supprimer"));
+    const confirm = await screen.findByRole("dialog", {
+      name: "confirmer la suppression",
+    });
+    fireEvent.click(within(confirm).getByLabelText("cancel delete"));
+
+    // The confirmation is dismissed, delete was never called, ticket stays.
+    await waitFor(() =>
+      expect(
+        screen.queryByRole("dialog", { name: "confirmer la suppression" }),
+      ).toBeNull(),
+    );
+    expect(delSpy).not.toHaveBeenCalled();
+    expect(
+      screen.getByRole("dialog", { name: `ticket ${t.ref}` }),
+    ).toBeTruthy();
+    const fresh = await ticket.read(PROJECT_ID, t.ref);
+    expect(fresh.title).toBe("Keeper");
+  });
+
   it("copies a delegation context prompt (F7)", async () => {
     const writeText = stubClipboard();
     const t = await ticket.create(PROJECT_ID, { title: "Delegate me" });