Every canvas position write (Auto-arrange, Save positions, drags, freeze pins)
used to send one PATCH per technology, all at once. On a large tree that was
dozens of concurrent full document updates, which exhausted the database pool
and could crash the server.
- Add POST /api/tech-tree/positions: validates `{ positions: [{ id, x, y }] }`
(null x/y clears a pin, capped at 2000) and applies every position in a
single UPDATE on the tree position columns. Access mirrors the technologies
update rule (technologies:update or Intelligence membership).
- Route all canvas position writes through it; failures now surface in the
toolbar instead of being swallowed.
- Auto-arrange is optimistic: the canvas re-lays out on click and the pins
are restored if the save fails. A spinner status chip shows while a layout
save runs, and layout controls and dragging are locked until it finishes.
- Integration tests for validation and the bulk write; the e2e checks the busy
indicator and that no per-node PATCHes are sent.
