feat: add transactions export command

[johann-taberlet]

Summary

Adds a new transactions subcommand to export account transactions over a date range, using BoursoBank's CSV export endpoint (/budget/exporter-mouvements).

# CSV output (default)
bourso transactions -a <account_id> -f "01/01/2026" -t "31/01/2026"

# JSON output
bourso transactions -a <account_id> -f "01/01/2026" -t "31/01/2026" -o json

Changes

• bourso_api::account: Add Transaction struct with all fields from BoursoBank CSV export
• bourso_api::client::transaction: Add get_transactions() method on BoursoWebClient
  • Hits the /budget/exporter-mouvements endpoint with date range and account filter
  • Handles the 302 redirect to api.boursobank.com for file download (since the client uses Policy::none())
  • Parses BoursoBank CSV format (semicolon-separated, French number format with comma decimals and space thousands separators)
  • Returns empty Vec gracefully when an HTML error page is returned
• CLI: Add transactions subcommand with --account, --from, --to, --output args
• New dependency: csv crate for robust CSV parsing

Test plan

• cargo build --release compiles without errors
• cargo test -p bourso_api — 11 tests pass (3 new: test_parse_amount, test_extract_transactions, test_extract_transactions_empty_html)
• Manual test: successfully exported 8 transactions from a live BoursoBank account with CSV output
• Manual test: JSON output (-o json) works correctly

[azerpas]

Thank you very much for the contribution @johann-taberlet

A few things top of my head:

• I feel like the command should be something like bourse-cli export transactions [...] so that we can have something similar for export orders or export transfers
• -f is often used to used for --format args, which I feel could be a good replacement to the current --ouput/-o
• same for -o/--ouput which often designate a file output. I feel like that would suit well an export to a json or csv file
• to replace -f/--from I would use --start-date and --end-date to make it really explicit
• With all these we'll have something like bourso export transactions -a <account_id> --start-date "01/01/2026" --end-date "31/01/2026" -f json -o /Users/johndoe/transactions.json. Wdyt?

[johann-taberlet]

Thanks for the feedback @azerpas! All changes implemented in the latest commit:

• bourso export transactions — moved under a new export subcommand, ready for future export orders, export transfers, etc.
• --start-date / --end-date — replaced --from/-f and --to/-t
• --format / -f — replaced --output/-o for format selection (csv/json)
• --output / -o — new optional arg for file output path (defaults to stdout)

Final usage:

bourso export transactions -a <account_id> --start-date "01/01/2026" --end-date "31/01/2026" -f json -o /path/to/transactions.json

All 11 tests still passing, build OK. Tested manually with both CSV (stdout) and JSON (stdout) output.