MPR008: name the loop box as the cause when a loop overlaps its neighbours, or let layout place loops #1690

What happens

MPR008 reports overlapping activities with the message "each statement needs its own @position". When the cause is a loop box that overlaps the activities before and after it, the message is misleading: giving every statement a position does not help. The loop box seems to grow with its x position, so a fixed gap that works at x 1200 overlaps at x 1280.

Expected

Either a loop-specific hint in MPR008 (name the loop and say its box overlaps), or mxcli layout placing loops so that the neighbours do not overlap (see also #1672 for error handlers).

Evidence

A flow with a loop between two activities, positioned by hand: MPR008 fires with the generic text. A fixed gap that is enough at x 1200 overlaps at x 1280.

Environment

mxcli 0.28.0, Studio Pro 11.12.4, Windows 11. Found by the AppGen tooling (Ciphix) on a test app.