Kalshi: ingest markets + time series snapshots

[nav-v]

Objective: Pull market metadata + current probability (or equivalent) from Kalshi and store as a structured df.

Acceptance criteria:

• function that returns a df with at least: platform, market_id, title, timestamp, price/prob
• saving these snapshots on a daily basis - potentially on supabase
• handles pagination + API errors (retry/backoff or graceful failure)