Test DB setup should follow standard Python load_dotenv convention #585

Problem

Tests connect to the dev database (ocotilloapi_dev) instead of the test database (ocotilloapi_test) because multiple load_dotenv(override=True) calls stomp env vars set by the test framework. There are 7 load_dotenv calls across the codebase with inconsistent override behavior:

The override=True calls re-read .env (which has POSTGRES_DB=ocotilloapi_dev) and overwrite the test framework's POSTGRES_DB=ocotilloapi_test.

Proposed fix: follow standard Python convention

The standard convention in the Python/FastAPI ecosystem:

1. load_dotenv() (no override) everywhere — .env provides defaults, not overrides. Env vars already set by the runtime, test framework, or CI take precedence. This is the default behavior of python-dotenv for a reason.

2. Set test env vars before load_dotenv() — in tests/__init__.py, set POSTGRES_DB=ocotilloapi_test before calling load_dotenv(). Since the default is no-override, .env's value won't stomp it.

3. One load_dotenv() per entry point — main.py, cli/cli.py, tests/__init__.py, transfers/transfer.py each call it once. Library code (db/engine.py) and Alembic (env.py) should NOT call load_dotenv() — they rely on the entry point having loaded it.

Concrete changes

• tests/__init__.py: set POSTGRES_DB=ocotilloapi_test before load_dotenv(), remove override=True
• tests/conftest.py: remove load_dotenv call entirely, remove TEST_DATABASE_NAME / _test_database_url()
• db/engine.py: remove load_dotenv(override=False) (entry points handle it)
• alembic/env.py: remove load_dotenv() (entry points handle it)
• cli/cli.py: change override=True to plain load_dotenv()
• transfers/transfer.py: simplify override=False to plain load_dotenv()
• main.py: already correct, no change