feat: add SQLite migration runner

src/fastapi_oidc_op/store/sqlite/migrations.py

@@ -0,0 +1,48 @@
+from pathlib import Path
+
+import aiosqlite
+
+
+async def run_migrations(db: aiosqlite.Connection, migrations_dir: Path) -> int:
+    """Apply unapplied SQL migration files in order. Returns count of newly applied migrations."""
+    if not migrations_dir.is_dir():
+        raise FileNotFoundError(f"Migrations directory not found: {migrations_dir}")
+
+    await db.execute(
+        """
+        CREATE TABLE IF NOT EXISTS _migrations (
+            id INTEGER PRIMARY KEY,
+            filename TEXT NOT NULL UNIQUE,
+            applied_at TEXT NOT NULL DEFAULT (datetime('now'))
+        )
+        """
+    )
+    await db.commit()
+
+    async with db.execute("SELECT filename FROM _migrations") as cursor:
+        applied = {row[0] async for row in cursor}
+
+    migration_files = sorted(migrations_dir.glob("*.sql"))
+
+    count = 0
+    for migration_file in migration_files:
+        if migration_file.name in applied:
+            continue
+        sql = migration_file.read_text(encoding="utf-8")
+        await db.execute("BEGIN")
+        try:
+            for statement in sql.split(";"):
+                statement = statement.strip()
+                if statement:
+                    await db.execute(statement)
+            await db.execute(
+                "INSERT INTO _migrations (filename) VALUES (?)",
+                (migration_file.name,),
+            )
+            await db.commit()
+        except Exception:
+            await db.rollback()
+            raise
+        count += 1
+
+    return count