Categorize Mapbox as Essential content for microG compatibility

[Copilot]

microG uses Mapbox as a Google Maps replacement. TrackerControl currently categorizes api.mapbox.com as "Uncategorised", breaking map functionality in apps unless users manually whitelist it per-app.

Changes

• Add "necessary": true flag to Mapbox entry in xray-blacklist.json
• Mapbox domains now categorized as "Content" (displayed as "Essential" in UI)

Technical Context

The tracker loader treats entries with "necessary": true as essential services:

// TrackerList.java, line 362
String category = necessary ? "Content" : UNCATEGORISED;

Subdomain matching automatically covers api.mapbox.com when mapbox.com is registered, so no additional domain entries needed.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Move api.mapbox.com into separate category for all apps</issue_title>
<issue_description>Thanks for this great app.

https://microg.org/ uses Mapbox as Google Maps replacement, so if you use microg, Mapbox is essential for a lot of different apps. This breaks most of the apps showing any kind of map. If I allow api.mapbox.com manually in all the apps, they work again.

For reference #160 , but on my phone with TrackerControl 2022.10.25-fdroid api.mapbox.com is in Uncategorized category.</issue_description>

Comments on the Issue (you are @copilot in this section)

@kasnder Good idea. Will look into this.

• Fixes Move api.mapbox.com into separate category for all apps #362

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