feat(meituan): 政治类文章拦截 + 写'无可奉告' + Angel 并发 3→1

- llm_settings 加 meituan_blocked_topics / blocked_keywords / no_comment_text
- alembic 0006 迁移,默认 topics=[时政/国际/军事/政治/战争/冲突/制裁/选举], 默认文案='无可奉告'
- enrichment._is_meituan_blocked 预检:category 命中 topic 或 关键词 → 直接写'无可奉告',不调美团 API
- 命中后 commentary_meituan_model='policy-block' 标识非真实生成
- enrichment_loop Semaphore(3)→(1),Agnes 免费 plan 不再 429
- 前端 AdminLlmSettings 美团卡片加 3 字段 UI(主题/关键词/固定文案)

backend/alembic/versions/0006_meituan_blocked_topics.py

@@ -0,0 +1,64 @@
+"""美团"无可奉告"主题清单 — 命中则不调美团 API,直接写固定文案
+
+- llm_settings.meituan_blocked_topics    JSONB  (默认 ["时政", "国际", "军事", "政治", "战争", "冲突", "制裁", "选举"])
+- llm_settings.meituan_blocked_keywords  JSONB  (默认 [])
+- llm_settings.meituan_no_comment_text    TEXT   (默认 "无可奉告")
+
+Revision ID: 0006
+Revises: 0005
+Create Date: 2026-06-12
+"""
+from __future__ import annotations
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+from sqlalchemy.dialects.postgresql import JSONB
+
+revision: str = "0006"
+down_revision: Union[str, None] = "0005"
+branch_labels = None
+depends_on = None
+
+
+DEFAULT_TOPICS = ["时政", "国际", "军事", "政治", "战争", "冲突", "制裁", "选举"]
+
+
+def upgrade() -> None:
+    import json
+    default_topics_json = sa.text(repr(json.dumps(DEFAULT_TOPICS, ensure_ascii=False)))
+
+    op.add_column(
+        "llm_settings",
+        sa.Column(
+            "meituan_blocked_topics",
+            JSONB,
+            nullable=False,
+            server_default=default_topics_json,
+        ),
+    )
+    op.add_column(
+        "llm_settings",
+        sa.Column(
+            "meituan_blocked_keywords",
+            JSONB,
+            nullable=False,
+            server_default=sa.text("'[]'::jsonb"),
+        ),
+    )
+    op.add_column(
+        "llm_settings",
+        sa.Column(
+            "meituan_no_comment_text",
+            sa.Text,
+            nullable=False,
+            server_default="无可奉告",
+        ),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("llm_settings", "meituan_no_comment_text")
+    op.drop_column("llm_settings", "meituan_blocked_keywords")
+    op.drop_column("llm_settings", "meituan_blocked_topics")