fix: make SQL echo configurable via env var instead of hardcoded True

[abhishek-8081]

What

Replaced hardcoded echo=True in api/db/database.py with an env var toggle (SQL_DEBUG). SQL echo is now off by default.

Why

echo=True prints every SQL query to stdout on every API request. This was probably left on from debugging but it makes the terminal output really noisy, especially when you're trying to debug something else. It also leaks query details which isn't great.

Changes

# Before
echo=True,

# After
echo=os.getenv("SQL_DEBUG", "false").lower() == "true",

To enable SQL logging when needed, just set the env var:

SQL_DEBUG=true uvicorn api.main:app --reload

Testing

• Verified SQL output is silent by default (no env var set)
• Verified SQL_DEBUG=true enables SQL logging as expected
• No other files depend on this setting

Fixes #372