fix(gymtracker): self-host Flatpickr for admin (avoid CDN/Access blocks)
Serve calendar UI assets from /vendor/flatpickr on gymtracker; Safari/WebKit
'permission' failures often trace to blocked jsDelivr or overly broad
Access paths. Document narrowing Access or bypass for /favicon and /vendor.
Note: flatpickr.min.Js is force-added (repo .gitignore ignores *.min.js).