refactor: Migrate database service to SQLModel and Alembic.

- Add SQLModel for type-safe database models
- Implement Alembic for schema migration management
- Create 7 migrations covering all existing schema changes
- Add automatic migration system that runs on startup
- Maintain backward compatibility with existing raw SQL queries
- Remove old manual migration system
- All tests pass (109 tests)

Benefits:
- Full type safety with Pydantic validation
- Version-controlled schema changes
- Automatic migration detection and application
- Better developer experience with typed models

alembic/versions/de8bfb1169d4_create_initial_tables.py

@@ -0,0 +1,95 @@
+"""create_initial_tables
+
+Revision ID: de8bfb1169d4
+Revises:
+Create Date: 2025-09-30 23:09:24.255875
+
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "de8bfb1169d4"
+down_revision: Union[str, Sequence[str], None] = None
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Create initial database tables."""
+    # Create accounts table
+    op.create_table(
+        "accounts",
+        sa.Column("id", sa.String(), nullable=False),
+        sa.Column("institution_id", sa.String(), nullable=False),
+        sa.Column("status", sa.String(), nullable=False),
+        sa.Column("iban", sa.String(), nullable=True),
+        sa.Column("name", sa.String(), nullable=True),
+        sa.Column("currency", sa.String(), nullable=True),
+        sa.Column("created", sa.DateTime(), nullable=False),
+        sa.Column("last_accessed", sa.DateTime(), nullable=True),
+        sa.Column("last_updated", sa.DateTime(), nullable=True),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index("idx_accounts_institution_id", "accounts", ["institution_id"])
+    op.create_index("idx_accounts_status", "accounts", ["status"])
+
+    # Create balances table
+    op.create_table(
+        "balances",
+        sa.Column("id", sa.Integer(), autoincrement=True, nullable=False),
+        sa.Column("account_id", sa.String(), nullable=False),
+        sa.Column("bank", sa.String(), nullable=False),
+        sa.Column("status", sa.String(), nullable=False),
+        sa.Column("iban", sa.String(), nullable=False),
+        sa.Column("amount", sa.Float(), nullable=False),
+        sa.Column("currency", sa.String(), nullable=False),
+        sa.Column("type", sa.String(), nullable=False),
+        sa.Column("timestamp", sa.DateTime(), nullable=False),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index("idx_balances_account_id", "balances", ["account_id"])
+    op.create_index("idx_balances_timestamp", "balances", ["timestamp"])
+    op.create_index(
+        "idx_balances_account_type_timestamp",
+        "balances",
+        ["account_id", "type", "timestamp"],
+    )
+
+    # Create transactions table (old schema with internalTransactionId as PK)
+    op.create_table(
+        "transactions",
+        sa.Column("accountId", sa.String(), nullable=False),
+        sa.Column("transactionId", sa.String(), nullable=False),
+        sa.Column("internalTransactionId", sa.String(), nullable=True),
+        sa.Column("institutionId", sa.String(), nullable=False),
+        sa.Column("iban", sa.String(), nullable=True),
+        sa.Column("transactionDate", sa.DateTime(), nullable=True),
+        sa.Column("description", sa.String(), nullable=True),
+        sa.Column("transactionValue", sa.Float(), nullable=True),
+        sa.Column("transactionCurrency", sa.String(), nullable=True),
+        sa.Column("transactionStatus", sa.String(), nullable=True),
+        sa.Column("rawTransaction", sa.JSON(), nullable=False),
+        sa.PrimaryKeyConstraint("internalTransactionId"),
+    )
+    op.create_index(
+        "idx_transactions_internal_id", "transactions", ["internalTransactionId"]
+    )
+    op.create_index("idx_transactions_date", "transactions", ["transactionDate"])
+    op.create_index(
+        "idx_transactions_account_date",
+        "transactions",
+        ["accountId", "transactionDate"],
+    )
+    op.create_index("idx_transactions_amount", "transactions", ["transactionValue"])
+
+
+def downgrade() -> None:
+    """Drop initial tables."""
+    op.drop_table("transactions")
+    op.drop_table("balances")
+    op.drop_table("accounts")