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。

reaction_board/services/library.py

@@ -302,6 +302,32 @@ class LibraryService:
             message=f"已拉黑 UP，并忽略该 UP 的 {rejected} 条待决策候选",
         )
 
+    # ------------------------------------------------------------ candidate admin
+
+    def pending_candidates(self) -> list[dict[str, Any]]:
+        return self.repo.list_pending_candidates()
+
+    def delete_candidate(self, aid: int) -> dict[str, Any] | None:
+        """删除单条候选；返回被删记录（不存在则 None）。"""
+        aid = int(aid)
+        candidate = self.repo.get_candidate(aid)
+        if candidate is None:
+            return None
+        self.repo.delete_candidate(aid)
+        self.repo.bump_cache_version("videos")
+        self._log("info", "candidate.delete", aid=aid)
+        return candidate
+
+    def clear_candidates(self, *, pending_only: bool = False) -> int:
+        """删除候选（``pending_only=True`` 只删待决策）；返回删除数。"""
+        removed = self.repo.delete_all_candidates(pending_only=pending_only)
+        if removed:
+            self.repo.bump_cache_version("videos")
+        self._log(
+            "info", "candidate.clear", pending_only=pending_only, removed=removed,
+        )
+        return removed
+
     # ------------------------------------------------------------ internals
 
     def _result_from_outcome(self, outcome, *, title: str, up_name: str) -> IngestResult: