v5.0.1 — a curated context names the water, not the town

Dodd Narrows reads Northumberland Channel instead of Nanaimo, and NAS Whidbey Island reads Strait of Juan de Fuca instead of Oak Harbor. A curated context names the water or landmark a station sits in; a town is what the derived tier already says, so Nanaimo next to Sidney, BC read as a derived label missing its province. Both towns stay in cities for search.

Validation now rejects a context that is one of the record's own cities, in both the registry and corrections validators. Data and validation only, no API change. Via #33.