feat(eval): Playground GLM 评分落库并可恢复

在 conversations 表增加 playground_conversation_judge_json，流式/非流式对话评审结束后写入最近一次快照（整体分、逐轮分、对比文案、错误与基线文件名等）。新增只读 GET 供前端按会话拉取；评测台 Playground 切换会话时自动恢复，并提示基线是否和当时一致。

api/alembic/versions/0013_conversations_playground_judge_json.py

@@ -0,0 +1,39 @@
+"""Persist Playground GLM conversation judge snapshot on conversations.
+
+Revision ID: 0013_playground_judge
+Revises: 0012_mem_fact_tl_lineage
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+from alembic import op
+
+revision: str = "0013_playground_judge"
+down_revision: Union[str, None] = "0012_mem_fact_tl_lineage"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def _has_column(table: str, column: str) -> bool:
+    bind = op.get_bind()
+    return any(c["name"] == column for c in sa.inspect(bind).get_columns(table))
+
+
+def upgrade() -> None:
+    if not _has_column("conversations", "playground_conversation_judge_json"):
+        op.add_column(
+            "conversations",
+            sa.Column(
+                "playground_conversation_judge_json",
+                postgresql.JSON(astext_type=sa.Text()),
+                nullable=True,
+            ),
+        )
+
+
+def downgrade() -> None:
+    if _has_column("conversations", "playground_conversation_judge_json"):
+        op.drop_column("conversations", "playground_conversation_judge_json")