New crypto bot type: creates a broadcast channel and posts a price snapshot of the
selected coins/currencies (CoinGecko simple/price JSON) every interval — same
channel-streaming model as RSS. Create form has checkbox grids for popular coins
and currencies plus a poll interval. Generalize the channel helper and feed-poll
state (channel_gid/poll_next) shared by rss + crypto. Adds crypto_test.py (mock
CoinGecko) — passes; rss_test updated for the renamed field.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
