migrate season files to episode files and drop legacy table (#454)

This pull request introduces a migration script to transition from
storing file information at the season level to the episode level in the
database.

alembic/versions/a6f714d3c8b9_migrate_season_files_to_episode_files.py

@@ -0,0 +1,71 @@
+"""migrate season files to episode files and drop the legacy table
+
+Revision ID: a6f714d3c8b9
+Revises: 16e78af9e5bf
+Create Date: 2026-02-22 16:30:00
+
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+from sqlalchemy.dialects import postgresql
+
+
+# revision identifiers, used by Alembic.
+revision: str = "a6f714d3c8b9"
+down_revision: Union[str, None] = "3a8fbd71e2c2"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Copy season_file records into episode_file and remove the legacy table."""
+    op.execute(
+        """
+        INSERT INTO episode_file (episode_id, torrent_id, file_path_suffix, quality)
+        SELECT episode.id, season_file.torrent_id, season_file.file_path_suffix, season_file.quality
+        FROM season_file
+        JOIN season ON season.id = season_file.season_id
+        JOIN episode ON episode.season_id = season.id
+        LEFT JOIN episode_file ON
+            episode_file.episode_id = episode.id
+            AND episode_file.file_path_suffix = season_file.file_path_suffix
+        WHERE episode_file.episode_id IS NULL
+        """
+    )
+    op.drop_table("season_file")
+
+
+def downgrade() -> None:
+    """Recreate season_file, repopulate it from episode_file, and keep both tables."""
+    quality_enum = postgresql.ENUM(
+        "uhd", "fullhd", "hd", "sd", "unknown", name="quality", create_type=False
+    )
+
+    op.create_table(
+        "season_file",
+        sa.Column("season_id", sa.UUID(), nullable=False),
+        sa.Column("torrent_id", sa.UUID(), nullable=True),
+        sa.Column("file_path_suffix", sa.String(), nullable=False),
+        sa.Column("quality", quality_enum, nullable=False),
+        sa.ForeignKeyConstraint(["season_id"], ["season.id"], ondelete="CASCADE"),
+        sa.ForeignKeyConstraint(["torrent_id"], ["torrent.id"], ondelete="SET NULL"),
+        sa.PrimaryKeyConstraint("season_id", "file_path_suffix"),
+    )
+
+    op.execute(
+        """
+        INSERT INTO season_file (season_id, torrent_id, file_path_suffix, quality)
+        SELECT DISTINCT ON (episode.season_id, episode_file.file_path_suffix)
+            episode.season_id,
+            episode_file.torrent_id,
+            episode_file.file_path_suffix,
+            episode_file.quality
+        FROM episode_file
+        JOIN episode ON episode.id = episode_file.episode_id
+        ORDER BY episode.season_id, episode_file.file_path_suffix, episode_file.torrent_id, episode_file.quality
+        """
+    )
+