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_library.py

@@ -326,6 +326,33 @@ def test_ignore_and_blacklist():
             db.close()
 
 
+def test_candidate_admin_delete_and_clear():
+    with tempfile.TemporaryDirectory() as tmp:
+        db, repo, service = setup(tmp, FakeReadClient())
+        try:
+            add_candidate(repo, 1)
+            add_candidate(repo, 2)
+            add_candidate(repo, 3)
+            repo.mark_candidate_decision(3, "rejected")
+
+            assert [c["aid"] for c in service.pending_candidates()] == [1, 2]
+
+            deleted = service.delete_candidate(2)
+            assert deleted is not None and deleted["aid"] == 2
+            assert repo.get_candidate(2) is None
+            assert service.delete_candidate(999) is None
+
+            assert service.clear_candidates(pending_only=True) == 1
+            assert repo.get_candidate(3) is not None  # 已决策保留
+            assert repo.get_candidate(1) is None
+
+            add_candidate(repo, 4)
+            assert service.clear_candidates() == 2  # aid 3 + aid 4
+            assert repo.list_candidates() == []
+        finally:
+            db.close()
+
+
 def main():
     test_ingest_candidate_added_and_snapshot()
     test_ingest_candidate_exists_and_missing()
@@ -337,6 +364,7 @@ def main():
     test_manual_ingest_truncation()
     test_manual_ingest_invalid_bvid_message()
     test_ignore_and_blacklist()
+    test_candidate_admin_delete_and_clear()
     print("OK: 入库、手动入库、忽略、拉黑测试全部通过")