feat(mail): 支持删除自定义文件夹并回收邮件

- 后端新增文件夹删除接口，禁止删除系统文件夹，并将文件夹内邮件自动移回收件箱。
- 前端补充删除文件夹的 API 调用、侧边栏菜单入口和确认弹窗。
- 增加测试覆盖删除自定义文件夹后的邮件回收与系统文件夹保护。

apps/api/internal/app/app_test.go

@@ -1047,6 +1047,59 @@ func TestCustomMailFoldersCreateAndMove(t *testing.T) {
 	}
 }
 
+func TestCustomMailFoldersDeleteMovesMessagesToInbox(t *testing.T) {
+	a := newTestApp(t)
+	ts := httptest.NewServer(a.Router())
+	defer ts.Close()
+	admin := &testClient{t: t, server: ts}
+
+	var login map[string]any
+	if code := admin.do("POST", "/api/auth/login", map[string]string{"email": "admin@lanqin.local", "password": "ChangeMe123!"}, &login); code != http.StatusOK {
+		t.Fatalf("login code=%d body=%v", code, login)
+	}
+	var custom MailFolder
+	if code := admin.do("POST", "/api/mail/folders", map[string]string{"name": "临时项目"}, &custom); code != http.StatusCreated {
+		t.Fatalf("create custom folder code=%d folder=%+v", code, custom)
+	}
+	var sent MailMessage
+	if code := admin.do("POST", "/api/mail/send", map[string]any{"to": []string{"person@example.test"}, "subject": "delete folder keeps message", "text": "body"}, &sent); code != http.StatusCreated {
+		t.Fatalf("send code=%d msg=%+v", code, sent)
+	}
+	var ok map[string]any
+	if code := admin.do("POST", "/api/mail/messages/"+sent.ID+"/move", map[string]string{"folder": "临时项目"}, &ok); code != http.StatusOK {
+		t.Fatalf("move to custom folder code=%d body=%v", code, ok)
+	}
+	if code := admin.do("DELETE", "/api/mail/folders/"+custom.ID, nil, &ok); code != http.StatusOK {
+		t.Fatalf("delete custom folder code=%d body=%v", code, ok)
+	}
+	var folders struct {
+		Items []MailFolder `json:"items"`
+	}
+	if code := admin.do("GET", "/api/mail/folders", nil, &folders); code != http.StatusOK || folderListContains(folders.Items, "临时项目") {
+		t.Fatalf("folder should be deleted code=%d items=%+v", code, folders.Items)
+	}
+	var inbox struct {
+		Items []MailMessage `json:"items"`
+	}
+	if code := admin.do("GET", "/api/mail/messages?folder=Inbox&q="+url.QueryEscape("delete folder keeps message"), nil, &inbox); code != http.StatusOK || len(inbox.Items) == 0 || inbox.Items[0].ID != sent.ID {
+		t.Fatalf("message should be moved to inbox code=%d items=%+v", code, inbox.Items)
+	}
+	var bad map[string]any
+	var inboxID string
+	for _, item := range folders.Items {
+		if item.Name == "Inbox" {
+			inboxID = item.ID
+			break
+		}
+	}
+	if inboxID == "" {
+		t.Fatalf("inbox id not found")
+	}
+	if code := admin.do("DELETE", "/api/mail/folders/"+inboxID, nil, &bad); code != http.StatusBadRequest {
+		t.Fatalf("delete system folder should be rejected code=%d body=%v", code, bad)
+	}
+}
+
 func TestCustomMailFoldersReorder(t *testing.T) {
 	a := newTestApp(t)
 	ts := httptest.NewServer(a.Router())

apps/api/internal/app/mail_handlers.go

@@ -249,6 +249,86 @@ func (a *App) handleCreateMailFolder(w http.ResponseWriter, r *http.Request) {
 	respondJSON(w, http.StatusCreated, folder)
 }
 
+func (a *App) handleDeleteMailFolder(w http.ResponseWriter, r *http.Request) {
+	mb, err := a.mailboxForCurrentUser(r)
+	if err != nil {
+		respondError(w, http.StatusNotFound, "mailbox not found")
+		return
+	}
+	folderID := strings.TrimSpace(chi.URLParam(r, "id"))
+	if folderID == "" {
+		badRequest(w, errors.New("folder id is required"))
+		return
+	}
+	var folderName string
+	if err := a.db.QueryRowContext(r.Context(), `SELECT name FROM folders WHERE id=? AND mailbox_id=?`, folderID, mb.ID).Scan(&folderName); err != nil {
+		if errors.Is(err, sql.ErrNoRows) {
+			respondError(w, http.StatusNotFound, "folder not found")
+			return
+		}
+		respondError(w, http.StatusInternalServerError, "failed to load folder")
+		return
+	}
+	if isSystemFolderName(folderName) {
+		badRequest(w, errors.New("system folders cannot be deleted"))
+		return
+	}
+	inboxID, err := a.ensureFolder(r.Context(), mb.ID, "Inbox")
+	if err != nil {
+		respondError(w, http.StatusInternalServerError, "failed to load inbox")
+		return
+	}
+	now := a.now().UTC().Format(time.RFC3339Nano)
+	tx, err := a.db.BeginTx(r.Context(), nil)
+	if err != nil {
+		respondError(w, http.StatusInternalServerError, "failed to delete folder")
+		return
+	}
+	defer tx.Rollback()
+	rows, err := tx.QueryContext(r.Context(), `SELECT id FROM messages WHERE mailbox_id=? AND folder_id=? ORDER BY received_at,id`, mb.ID, folderID)
+	if err != nil {
+		respondError(w, http.StatusInternalServerError, "failed to load folder messages")
+		return
+	}
+	var messageIDs []string
+	for rows.Next() {
+		var id string
+		if err := rows.Scan(&id); err != nil {
+			rows.Close()
+			respondError(w, http.StatusInternalServerError, "failed to scan folder messages")
+			return
+		}
+		messageIDs = append(messageIDs, id)
+	}
+	if err := rows.Err(); err != nil {
+		rows.Close()
+		respondError(w, http.StatusInternalServerError, "failed to scan folder messages")
+		return
+	}
+	rows.Close()
+	for _, messageID := range messageIDs {
+		meta, err := a.nextIMAPMetadata(r.Context(), tx, inboxID)
+		if err != nil {
+			respondError(w, http.StatusInternalServerError, "failed to allocate message uid")
+			return
+		}
+		if _, err := tx.ExecContext(r.Context(), `UPDATE messages SET folder_id=?,imap_uid=?,imap_modseq=?,updated_at=? WHERE id=?`, inboxID, meta.UID, meta.ModSeq, now, messageID); err != nil {
+			respondError(w, http.StatusInternalServerError, "failed to move folder messages")
+			return
+		}
+	}
+	if _, err := tx.ExecContext(r.Context(), `DELETE FROM folders WHERE id=? AND mailbox_id=?`, folderID, mb.ID); err != nil {
+		respondError(w, http.StatusInternalServerError, "failed to delete folder")
+		return
+	}
+	if err := tx.Commit(); err != nil {
+		respondError(w, http.StatusInternalServerError, "failed to delete folder")
+		return
+	}
+	_, _ = a.bumpFolderModSeq(r.Context(), inboxID)
+	respondJSON(w, http.StatusOK, map[string]any{"ok": true, "moved": len(messageIDs)})
+}
+
 func (a *App) ensureCustomFolder(ctx context.Context, mailboxID, name string) (string, error) {
 	return a.ensureFolder(ctx, mailboxID, name)
 }

apps/api/internal/app/router_auth.go

@@ -67,6 +67,7 @@ func (a *App) Router() http.Handler {
 			r.With(a.requirePermission(PermissionMailRead)).Get("/mail/folders", a.handleMailFolders)
 			r.With(a.requirePermission(PermissionMailOrganize)).Post("/mail/folders", a.handleCreateMailFolder)
 			r.With(a.requirePermission(PermissionMailOrganize)).Post("/mail/folders/reorder", a.handleReorderMailFolders)
+			r.With(a.requirePermission(PermissionMailOrganize)).Delete("/mail/folders/{id}", a.handleDeleteMailFolder)
 			r.With(a.requireAnyPermission(PermissionMailRead, PermissionMailLabels)).Get("/mail/labels", a.handleMailLabels)
 			r.With(a.requirePermission(PermissionMailLabels)).Post("/mail/labels", a.handleCreateMailLabel)
 			r.With(a.requirePermission(PermissionMailLabels)).Delete("/mail/labels/{id}", a.handleDeleteMailLabel)