feat(telegram): candidate list/delete/clear commands

私聊新增 /candidate [页码]（待决策列表）、/candi_del（标题按钮逐条删除，删后原地重建键盘、可翻页连续删）、/candi_clear（全部/待决策/取消）。重构 handle_callback 为前缀分派（cdel/cpage/cclr，保留 add/ign/blk/fav）；repository 加 list_pending_candidates/delete_all_candidates；LibraryService 加 pending_candidates/delete_candidate/clear_candidates 并刷看板缓存。

tests/test_candidates.py

@@ -180,11 +180,33 @@ def test_fav_action_state_machine():
             db.close()
 
 
+def test_list_pending_and_delete_all():
+    with tempfile.TemporaryDirectory() as tmp:
+        db, repo = setup(tmp)
+        try:
+            candidate(repo, 1, score=9)
+            candidate(repo, 2, score=4)
+            candidate(repo, 3, score=1)
+            repo.mark_candidate_decision(3, "rejected")
+
+            assert [c["aid"] for c in repo.list_pending_candidates()] == [1, 2]
+            assert repo.delete_all_candidates(pending_only=True) == 2
+            assert repo.get_candidate(3) is not None
+            assert repo.list_pending_candidates() == []
+
+            candidate(repo, 4)
+            assert repo.delete_all_candidates() == 2  # aid 3 + aid 4
+            assert repo.list_candidates() == []
+        finally:
+            db.close()
+
+
 def main():
     test_seen_and_known_aid()
     test_candidate_upsert_preserves_decision_and_notified()
     test_notify_and_reject_for_up()
     test_delete_expired_candidates_only_pending()
+    test_list_pending_and_delete_all()
     test_folder_for_up_uses_earliest_video()
     test_fav_action_state_machine()
     print("OK: 候选池、去重、通知记录与 fav_action 状态机测试全部通过")