feat(migration): add tts_audio_urls column to segments and conversation_messages tables

This migration introduces the 'tts_audio_urls' column to both the 'segments' and 'conversation_messages' tables, addressing a discrepancy between the ORM model and the production database. The upgrade function checks for the existence of these columns and adds them if they are missing, while the downgrade function allows for their removal if necessary.

api/alembic/versions/0020_add_tts_audio_urls_column.py

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+"""补建缺失列：segments.tts_audio_urls, conversation_messages.tts_audio_urls
+
+0001 用 create_all 建表，对已有表不会 ALTER 追加列。
+本迁移补齐 ORM 模型中存在但生产库缺失的 tts_audio_urls 列。
+
+Revision ID: 0020_add_tts_audio_urls_column
+Revises: 0019_backfill_missing_columns
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+
+from alembic import op
+
+revision: str = "0020_add_tts_audio_urls_column"
+down_revision: Union[str, None] = "0019_backfill_missing_columns"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def _column_names(table_name: str) -> set[str]:
+    bind = op.get_bind()
+    inspector = sa.inspect(bind)
+    return {column["name"] for column in inspector.get_columns(table_name)}
+
+
+def upgrade() -> None:
+    seg_cols = _column_names("segments")
+    if "tts_audio_urls" not in seg_cols:
+        op.add_column(
+            "segments",
+            sa.Column("tts_audio_urls", sa.JSON(), nullable=True),
+        )
+
+    msg_cols = _column_names("conversation_messages")
+    if "tts_audio_urls" not in msg_cols:
+        op.add_column(
+            "conversation_messages",
+            sa.Column("tts_audio_urls", sa.JSON(), nullable=True),
+        )
+
+
+def downgrade() -> None:
+    msg_cols = _column_names("conversation_messages")
+    if "tts_audio_urls" in msg_cols:
+        op.drop_column("conversation_messages", "tts_audio_urls")
+
+    seg_cols = _column_names("segments")
+    if "tts_audio_urls" in seg_cols:
+        op.drop_column("segments", "tts_audio_urls")