Problem: :Pending sync hardcodes Google Calendar — M.sync() does
pcall(require, 'pending.sync.gcal') and calls gcal.sync() directly.
The config has a flat gcal field. This prevents adding new sync backends
without modifying init.lua.
Solution: Define a backend interface contract (name, auth, sync, health
fields), refactor :Pending sync to dispatch via require('pending.sync.'
.. backend_name), add sync table to config with legacy gcal migration,
rename gcal.authorize to gcal.auth, add gcal.health for checkhealth,
and add tab completion for backend names and actions.
Barrett Ruth
7de9c23ec1