feat(db): 0003 migration + LlmSetting/Source 模型加 blocklist_tags

- 新增 alembic 0003: sources.blocklist_tags + llm_settings.blocklist_tags(JSONB)
- 两层配置:全局(llm_settings) + per-source(sources),合并去重后注入 classify prompt
- 默认空数组,不影响存量数据;admin API 在下个 commit 暴露编辑入口

backend/app/models/source.py

@@ -14,6 +14,7 @@ from sqlalchemy import (
     Text,
     func,
 )
+from sqlalchemy.dialects.postgresql import JSONB
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.database import Base
@@ -50,6 +51,10 @@ class Source(Base):
     language_src: Mapped[str | None] = mapped_column(String(8))
     priority: Mapped[int] = mapped_column(Integer, default=50, nullable=False, index=True)
     headers_json: Mapped[dict | None] = mapped_column(JSON)
+    # 源级屏蔽分类标签(如 ["体育", "娱乐"]);与 llm_settings.blocklist_tags 合并后使用
+    blocklist_tags: Mapped[list[str]] = mapped_column(
+        JSONB, nullable=False, default=list, server_default="[]"
+    )
     last_fetched_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
     last_status: Mapped[str | None] = mapped_column(String(64))
     consecutive_failures: Mapped[int] = mapped_column(Integer, default=0, nullable=False)