Queues, slots and the calendar

Each connected account can carry a posting schedule: a timezone and wall-clock slot times per weekday (for example weekdays at 11:00 and 17:00 in America/Los_Angeles). Slots are anchored in local time, so daylight-saving changes never move the local meaning of a slot.

• Add to queue (mode: queue) assigns the next free slot of the chosen account. Two posts added at the same moment never share a slot.
• Manual time always wins. A post scheduled at an explicit instant keeps it and occupies that slot if it lands on one.
• Slips. If a queued post is not publishable when its slot arrives (still a draft, awaiting approval, held), it moves to the next free slot. Nothing else moves: the posts around it keep their slots, and the post is never dropped.
• Swaps are explicit: swap two posts' instants, move a post to the next free slot, or set a manual time — from the post page or POST /posts/{id}/reschedule.
• The calendar (GET /calendar) lists every day's posts and every account's slots, taken or free; the account's queue view shows upcoming slots with their posts.