Personal Finance Tracker

Problem/Feature Description

Build a personal finance tracking API with Python and Flask. Use SQLite for storage (this is a single-user desktop app).

The system needs:

• Accounts: name, type (checking/savings/credit/cash), current balance in dollars, currency (default USD).
• Transactions: each transaction belongs to one account and has an amount in dollars, type (income/expense/transfer), category (groceries, rent, salary, etc.), description, and date.
• Transfers: moving money between two accounts. The source account balance decreases and the destination account balance increases by the same amount. Both balance updates and the transaction records must be saved together -- if any part fails, nothing should change.
• Monthly summary: total income, total expenses, and net change grouped by category for a given month.
• Record a transaction: create a transaction record and update the account balance atomically.
• Import transactions from CSV: accept a CSV file with date, amount, category, description columns and import all rows for a given account. If any row is malformed, reject the entire import.

Output Specification

Produce:

• app/database.py -- Database connection and schema
• app/models.py -- Pydantic models for request/response
• app/routes.py -- Flask route handlers
• app/app.py -- Flask application setup
• requirements.txt -- With dependencies

Complete Python code, no placeholders or TODO comments.