noshtastic-sync: need to constrain sync domain geographically

[ksedgwic]

This might be much easier than it seems:

• need some client support to insert geohash tags in signed messages
• need some nostrdb support to query with geohash prefixes

Nodes can have different configured geographic domains, need to include in negentropy messages and intersect (easy)

[ksedgwic]

Amethyst supports adding geohash tags to posts (there is a glyph in the new post UI to add, near the add photo, add, tag, etc). Generated events look like:

{"kind":1,"id":"f24e60e6ab99a83fb53182a61a2fbe44cb9ae532c36e9b73a31368f1b35c2b7c","pubkey":"850605096dbfb50b929e38a6c26c3d56c425325c85e05de29b759bc0e5d6cebc","created_at":1737223025,"tags":[["g","9q9p3"],["g","9q9p"],["g","9q9"],["g","9q"],["g","9"]],"content":"This post should have an amethyst geohash tag","sig":"81d7fb028f1b8bfede4eb93cde05548f90cbacf951315c64ee9cf446939991fae9ed009f8b8b69dc7b496fa5f1fb08470c34269c2cb6641e040e530382132fdc"}