feat(api): 接入智谱 embedding-3（1024 维）并迁移 memory_chunks 向量列

api/alembic/versions/0004_memory_chunks_embedding_vector_1024.py

@@ -0,0 +1,32 @@
+"""memory_chunks.embedding: vector(1536) -> vector(1024)，并清空旧向量。
+
+与智谱 embedding-3（固定 1024 维）及 ORM 一致；旧 OpenAI 等模型向量不可与智谱混用，故先置 NULL 再改类型。
+
+Revision ID: 0004_memory_embedding_1024
+Revises: 0003_timeline_memory_source
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+
+from alembic import op
+
+revision: str = "0004_memory_embedding_1024"
+down_revision: Union[str, None] = "0003_timeline_memory_source"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.execute(sa.text("UPDATE memory_chunks SET embedding = NULL"))
+    op.execute(
+        sa.text("ALTER TABLE memory_chunks ALTER COLUMN embedding TYPE vector(1024)")
+    )
+
+
+def downgrade() -> None:
+    op.execute(sa.text("UPDATE memory_chunks SET embedding = NULL"))
+    op.execute(
+        sa.text("ALTER TABLE memory_chunks ALTER COLUMN embedding TYPE vector(1536)")
+    )