v2.1.0 — edgeports.py: fix stacked edges on swimlanes

Added

scripts/edgeports.py — deterministic edge port assignment. The real replacement for the --layout libavoid flag removed in 2.0.0.

The problem

draw.io's floating connections attach every edge to the middle of whichever side faces the peer. Give a node three connections leaving its east side and all three land on the same point — they stack into what looks like one line. Most visible on swimlane / cross-functional flowcharts, where handoff edges between lanes share long orthogonal corridors (#96).

What it does

python3 edgeports.py diagram.drawio            # in place
python3 edgeports.py diagram.drawio --dry-run  # report only

1. Resolves every vertex to absolute coordinates, through swimlane/container parents — a step at x=0 inside a lane is not at the west edge of the page.
2. Picks the side of each node facing the other endpoint.
3. Groups ends by (node, side) and sorts each group by the far endpoint's position — so two edges leaving the same side keep their relative order instead of crossing.
4. Spreads them over evenly-spaced slots: k ends get 1/(k+1) … k/(k+1).

Ends you pinned by hand are skipped, so hand-tuned geometry survives. Re-running is a no-op.

Scope — read this before expecting too much

It is a port assigner, not a router. It separates lines where they meet a shape. It does not stop an edge crossing an unrelated shape mid-run — add <Array as="points"> waypoints for that, or open the file in draw.io desktop and use its editor-side obstacle-avoiding router.

Note also that validate.py --score cannot measure this change: it only scores edges carrying explicit waypoints, and port-pinned edges have none. It reports 0 before and after.

Verified on a 3-lane swimlane — 8 ends pinned, stacked handoffs separated, idempotent on re-run. Ships a --demo self-check covering parent-offset resolution, no-crossing ordering, and idempotency.

Closes #96 · released in #100.