Allow polygon and spline startboxes alongside legacy rectangles

[burnhamrobertp]

Closes #605

Summary

Widens the startbox poly schema to accept either the legacy 2-point rectangle (current shape every existing map ships) or an N-point polygon ring with optional Catmull-Rom spline strength per anchor. Discriminated via JSON Schema oneOf so existing data validates unchanged. Generators that target rect-only consumers (TEIServer's Tachyon protocol, SPADS' mapBoxes.conf) compute a bounding-box rectangle from polygon vertices; the polygon shape is preserved through gen_lobby_maps.ts for the polygon-aware new lobby and through sync_to_webflow.ts's existing startpos-code field unchanged.

Changes

schemas/map_list.yaml

• Replaced inline poly definition with oneOf: [startboxRect, startboxPolygon]
• New $defs.startboxRect — exactly 2 points, top-left/bottom-right corners (the existing format)
• New $defs.startboxPolygon — 3+ points, each with optional strength in [0, 1] for Catmull-Rom spline tessellation
• Range-only validation on strength. No multipleOf constraint to avoid float-comparison flakiness across validators; the Rowy editor enforces a 0.025 snap step at write time

scripts/js/src/check_startboxes.ts

• Branch on poly.length === 2
• Rectangle branch keeps the existing corner-ordering check
• Polygon branch checks for non-degenerate area via the shoelace formula

scripts/js/src/gen_teiserver_maps.ts

• New rectifyStartboxes() helper collapses N-point polygons to bounding-box rectangles before writing teiserver_maps.json — TEIServer's data model and Tachyon protocol stay rect-only

scripts/js/src/gen_map_boxes_conf.ts

• New polyToRectCorners() helper applies the same bounding-box fallback for SPADS' mapBoxes.conf format

gen_lobby_maps.ts (no change)

• bar-lobby is the polygon-aware consumer; the schema's poly passes through unchanged

Verification

• All 942 existing rectangle entries across all maps validate against the new schema (Python jsonschema + Draft 2020-12)
• Synthetic polygon (no strength) and synthetic spline (mixed strengths including 0.025 and 1) both validate
• Counter-tests rejected as expected: 1-point poly, strength: 2, 2-point poly with strength on a corner, polygon with extra property

Related PRs

• Core Game - Polygon startboxes via mapmetadata modoptions Beyond-All-Reason#7513
• Chobby Lobby - Polygon startbox infrastructure (rendering, encoder, modoption injection) BYAR-Chobby#1184
• New Lobby - Allow polygon start boxes bar-lobby#574
• New Lobby (active follow-up, amends Update all maps from rowy #574): Send polygon startboxes to the game bar-lobby#601
• Rowy editor Fork - Add polygon startbox column type p2004a/rowy#1

AI / LLM usage statement

Claude Opus 4.7 used to assist in implementation, schema design, and validation.