feat: Markdown report generator (python cli.py report)

[jakduch]

What does this add and why do you believe it belongs in this dashboard?

Adds python3 cli.py report — a Markdown usage-report generator that turns the same data the dashboard renders into a self-contained, copy-pasteable summary you can drop straight into chat, an issue, a stand-up note, or a PR description.

The existing CLI surface (today, week, stats) is great for a quick glance in the terminal, but the output is ANSI-coloured tables that don't travel — sharing them means screenshots of the dashboard or hand-typed numbers. A personal usage dashboard isn't only useful when you're looking at it; the moments that matter are the ones where you need to explain here's what my week on Claude actually cost to a teammate, a manager paying the bill, or your future self in a budget thread. Markdown is the lingua franca of those venues. One command, python cli.py report --period 7d, produces a clean section with totals, by-model and by-tool breakdowns, ready to paste. It fills the gap between the live dashboard and any asynchronous conversation about cost — no new dependencies, no new files outside cli.py and tests/.

Sample invocations:

python3 cli.py report                          # 30-day report to stdout
python3 cli.py report --period 7d                  # last week
python3 cli.py report --period all --out usage.md  # write to file

Changes:

• New helpers _period_bounds(period) and _in_range(day, start, end) in cli.py
• New build_report(period, db_path=None) pulls dashboard data and adds a by-tool breakdown
• New cmd_report(period, out) CLI entry — prints to stdout, or writes to --out FILE
• Supports --period 7d|30d|all (default 30d)
• Graceful: a missing DB still produces a valid markdown skeleton with zeroed totals
• Wired into USAGE, COMMANDS, and main() dispatch
• tests/test_report.py — 18 new unit tests covering period bounds, empty-DB skeleton, seeded-DB content, file-output flow, and CLI registration

Checklist

Code correctness

• All calcCost() calls pass 6 arguments: (model, inp, out, cache_read, cache_creation, cache_1h)
• JavaScript template literals use bare backticks (`), not escaped ones (\`)
• No JS variables referenced before they are defined
• No new third-party dependencies introduced

Tests

• python3 -m unittest discover -s tests -v — all passing (208 ran, 6 skipped)
• python3 -m unittest tests.test_browser -v — no such module on this branch; full discover suite green instead
• New behaviour is covered by at least one test

Scope

• This is a single concern — one feature or fix per PR
• Only touches existing files (dashboard.py, scanner.py, cli.py, pricing.py, cowork.py, tests/) — or I've explained below why a new file is needed

Note: tests/test_report.py is new — required to cover the new build_report / cmd_report surface; all other changes are confined to cli.py.