Add blocked_date table (migration 5), model, and store CRUD methods.
Add management page at /blocked with add/delete functionality.
Add nav link 'Terminy zablokowane' with event_busy icon.
Pass blocked dates to order form as JSON data attribute.
On form submit, if the order has special cakes and the date is
blocked, show a confirm() dialog warning the user.
Change terminal status from 'done' to 'picked_up' in all queries.
Add dateRangeParams helper, GetOrderCounts, GetCakeCounts.
Load special cakes in getOrdersFromQuery, save in UpdateOrderContents.
Seed: 5 tags, 3 special cakes, Maria status 'done'->'ready'.
Test: 'Done'->'ready'.
