Two complementary cache-busting strategies for the stale cron skill picker:
1. On cron form open (toggleCronForm): always null _cronSkillsCache before
fetching, so freshly created skills are immediately visible without a
page reload. Previously the cache was only populated once and never
invalidated.
2. On skill save (submitSkillSave): null _cronSkillsCache after a successful
write so the next cron form open is forced to re-fetch. Mirrors the
existing _skillsData=null pattern one line above.
Fixes: #502
Co-authored-by: armorbreak001 <armorbreak001@users.noreply.github.com>
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