geocoding improvements

[redshiftzero]

One of the weaknesses of the current approach is geocoding can fail for a particular center, and then that detention center won't be represented on the map, leading to missing data. These show up in the geocoded facilities file with longitude/latitude as null. Example: https://github.com/lockdown-systems/icewatch/blob/main/data/facilities_geocoded_20260203_154037.json#L126-L127

There are also facilities that have "unavailable" as the address. Some of these could perhaps be located through other means and we could include them manually. Example: https://github.com/lockdown-systems/icewatch/blob/main/data/facilities_geocoded_20260203_154037.json#L2324

We should do several things:

• Add an API key for the fallback provider (Mapbox) in CI
• Display somewhere on the site the detention centers that we don't have addresses for (and potentially ask for information)

Other ideas welcome!