Patch Notes: Harbour contracts go to real ports

Fixes

The harbourmaster's cargo contracts now send you only to port towns on the sea. They used to name tombs, farms, inns, temples, manors and ruins (most cargoes went to one), and region capitals far inland where no ship can reach.
A harbourmaster's board now stands only in a port town, never at a tomb's or a farm's shore.
A cargo you already hold for such a place is cancelled with a notice ("Contract void - ... No ship can make port there."), and your standing with the crown is unchanged.

FIELD BUGS 2026-10-13c PORT-TOWNS: the harbour board's ports are towns, and a cargo goes to one on the sea by @Lattymoy in #876

Full Changelog: app-v0.1.8455...app-v0.1.8457