Query from file with -f/--file flag

[vmvarela]

Description

Read the SQL query from a file instead of the command line.

Examples

sql-pipe -f analysis.sql data.csv
# or
cat data.csv | sql-pipe -f analysis.sql

Acceptance Criteria

• -f <file> / --file <file> reads SQL query from file
• Works with both file arguments and stdin input
• Error message if file doesn't exist or can't be read
• All existing tests pass
• New tests cover file-based queries

Notes

• Implementation: ~20 lines
• Pure upside, no trade-offs
• Universally understood pattern (every SQL CLI tool supports this)