Split a campaign budget across channels whose response only kicks in above a minimum spend

# Allocate the campaign budget across channels Inputs: `channels.csv` (channel, units, expected_signups: the expected signups when the channel gets that many budget units; a channel with 0 units gives 0) and `budget.json` (`units`: how many whole units to allocate, `max_units`: per-channel cap). Rules: - Every unit is a whole unit; a channel can get 0 units up to its cap. Units not listed for a channel are not allowed for that channel. - Spend at most the budget. Choose the allocation with the highest total expected signups. The data has exactly one best allocation. - Response is not linear: some channels give little or nothing until they reach a minimum spend. - what_if_signups = the best total if the budget had 2 more units (same caps). Write `out/allocation.json`: `{"allocation": {"<channel>": <units>, ...}, "total_signups": <int>, "units_used": <int>, "what_if_signups": <int>}`. List every channel, including those with 0. ## How this run works - Work on your own: nobody will answer questions in this task, and writing to `ask/` counts against the run. - Write only under `out/`. Create `out/` if it is missing. Inputs are synthetic; don't fetch anything from the network. - Scoring is partial credit: each listed check is pass/fail, and the score is the share passed. Numbers are compared to within 0.005 unless the task says otherwise.