[Bounty $500] Bank Sync Connector Architecture — pluggable bank integrations

[zhangyei1976-dotcom]

Bank Sync Connector Architecture — Issue #75

Implements a pluggable bank integration system for FinMind.

Architecture

connectors/
├── __init__.py       # Public API exports
├── base.py           # Abstract BankConnector + BankTransaction dataclass
├── mock.py           # MockBankConnector — synthetic data for dev/test
└── manager.py        # ConnectorManager — registry, import, refresh

Connector Interface (base.py)

• BankConnector — Abstract base class with three required methods:
  • fetch_transactions(user_id, from_date, to_date, **credentials) → list[BankTransaction]
  • refresh_connection(**credentials) → bool
  • get_connection_status() → dict
• BankTransaction — Normalized dataclass with to_expense_dict() for DB insertion

Mock Connector (mock.py)

• Returns 12 synthetic transactions across groceries, salary, utilities, etc.
• Spread over configurable date range
• Always returns healthy — perfect for CI and demos

Connector Manager (manager.py)

• register(connector) / unregister(name) — dynamic connector registry
• import_transactions(name, user_id, ...) — fetch + normalize
• refresh(name, user_id, ...) — verify connection + re-import
• Global singleton via get_connector_manager()

API Routes (routes/connectors.py)

• GET /api/connectors/ — list all registered connectors
• GET /api/connectors/<name>/status — connection health
• POST /api/connectors/<name>/import — import transactions
• POST /api/connectors/<name>/refresh — refresh + re-import

Adding a Real Bank

class HDFCBankConnector(BankConnector):
    name = "hdfc"
    display_name = "HDFC Bank"

    async def fetch_transactions(self, user_id, from_date, to_date, **creds):
        # Call HDFC API with creds["api_key"]
        ...

Closes #75