feat: detect road tiles via crosser metadata for surface speed

[plenarius]

Summary

• Detects road tiles at runtime using tileset crosser edge metadata instead of requiring walkmesh repaints for every tileset
• When a player steps on DIRT (1) or STONE (4), checks if the tile has crosser edges — if any edge is not in an exclusion list, promotes the surface to DIRTPATH/STONEPATH for the +33% speed bonus
• Loads a configurable exclusion file at startup (NWNX_LAYONARA_CROSSER_EXCLUSIONS_FILE) listing non-road crosser names (streams, cliffs, walls) so they don't get false road speed

Test plan

• Deploy to ee64, set NWNX_LAYONARA_CROSSER_EXCLUSIONS_FILE env var, place exclusions file on data mount
• Walk on roads in Windjammer's Bay (ttz01) — should get +33% speed
• Walk on roads in Dapplegreen Outskirts (wsf10) — should get +33% speed
• Walk on forest floor next to a road — should NOT get speed boost
• Walk along a stream — should NOT get speed boost (if stream crosser is in exclusions)
• Verify areas with repainted DIRTPATH walkmeshes still work (e.g., ttu01 areas)