docs(drone-airspace): correct the share token, voice support and coverage

The changelog fragment named share-link token 6 (sea marks); the layer
reserves 8. CURRENT-STATE said voice could toggle and query the layer and
listed it among the analyst record sources, but it is in VOICE_OFF_LAYERS.
Say voice is off for now, and that the layer covers FAA prohibited and
restricted special-use airspace only, not the UAS Facility Map / LAANC grids
or TFRs. A test pins these claims to the token ledger and the voice manifest.

changelog.d/1086-prohibited-restricted-airspace.md

@@ -5,4 +5,4 @@
   prohibited, orange restricted); selection shows name, altitude range, times
   of use and agency, and the row legend states the layer is informational only
   and does not include the UAS Facility Map or UAS flight restrictions. Off by
-  default; share-link token `6` (mvanhorn, #1086).
+  default; share-link token `8` (mvanhorn, #1086).