data-private/ is born: datasets whose publication could help close doors stay
out of the web-root and out of public repos, permanently. field-access-visas
moved there; the tables index no longer lists it; the key-cities Field Access
tab is removed from the public build; the table generator routes it (and any
future PRIVATE_TABLES entry) to data-private/ and excludes it from the index.
Public-good data (internet gaps, gospel-resource gaps, people-group pairings)
ships as before.
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