fix: ruff lint errors and broken migration down_revision

- Remove unused imports (field_validator, alembic.op)
- Fix unsorted imports in matching.py
- Fix merge_heads migration referencing non-existent 20260227_empty_wishlist revision

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: jeffcrouse

backend/app/api/routes/playlists.py

@@ -3,7 +3,7 @@
 from uuid import UUID
 
 from fastapi import APIRouter, Body, HTTPException, Query, status
-from pydantic import BaseModel, Field, field_validator
+from pydantic import BaseModel, Field
 from sqlalchemy import delete, func, select, update
 from sqlalchemy.orm import selectinload
 

backend/app/services/export_import/matching.py

@@ -5,14 +5,13 @@
 """
 
 import logging
+import re
 from typing import Any
 
 from rapidfuzz import fuzz
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
-import re
-
 from app.db.models import Track
 from app.utils.time import utcnow
 

backend/migrations/versions/20260306_merge_heads.py

@@ -1,14 +1,13 @@
-"""Merge wishlist and drop-features heads.
+"""Pin head after feature shelf removals.
 
 Revision ID: 20260306_merge_heads
-Revises: 20260227_empty_wishlist, 20260306_drop_spt_ext
+Revises: 20260306_drop_spt_ext
 Create Date: 2026-03-06
 """
 
-from alembic import op
 
 revision = "20260306_merge_heads"
-down_revision = ("20260227_empty_wishlist", "20260306_drop_spt_ext")
+down_revision = "20260306_drop_spt_ext"
 branch_labels = None
 depends_on = None