feat: add a calendar card reading khal

The month grid with the week's appointments below it, colour-coded by
calendar. Events come from a cache file rather than a live call: khal
costs about 200ms of Python startup, which is two orders of magnitude
over the 2-second draw budget, so bin/calendar-sample.sh writes the
cache on a 5-minute execi and the widget only parses.

Calendar colours are read out of khal's own config by the sampler and
mapped onto the board's palette roles, so the card follows a scheme
change instead of pinning three literal hues.

khal will not emit an ISO date: {start-date} uses the user's dateformat,
which carries no year here, and a strftime spec inside the field raises.
The sampler asks for {start-date-long} and data.calendar_date recovers
the numbers by position, resolving day/month by magnitude and reading a
genuinely ambiguous pair day-first. A 2-digit year is refused rather
than guessed at.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

0 files changed, 0 insertions, 0 deletions