Move the changelog entry into changelog.d and note seed and datasheet fallbacks

Main takes release notes as one fragment per pull request (#787). A missing value still falls back to a matching seed camera, and a datasheet can still set the field of view.

docs/CURRENT-STATE.md

@@ -1355,11 +1355,13 @@ browser rendering is unchanged.
 CCTV numbers are read as missing when they are absent, null, blank or boolean,
 on the server (`toFiniteNumber`, every pack and the file/env source packs) and
 in the browser (`safeNumber`). `/api/cctv/sources` sends an unknown number as
-JSON null; the browser then applies the field's default — id-hash heading,
-pitch −17°, FOV 74°, range 700 m, mount 24 m, the city's ground elevation —
-rather than reading zero and clamping it to the field's floor. A camera with a
-missing latitude or longitude is skipped by the browser catalog instead of
-being placed at 0,0. Real zeros, including `"0"`, are kept.
+JSON null; the browser then uses the bundled seed camera's value when one
+shares the id, else the field's default — id-hash heading, pitch −17°, FOV 74°
+(which a matched datasheet can still replace), range 700 m, mount 24 m, the
+city's ground elevation — rather than reading zero and clamping it to the
+field's floor. A camera with a missing latitude or longitude and no seed
+position is skipped by the browser catalog instead of being placed at 0,0.
+Real zeros, including `"0"`, are kept.
 
 ## Terrain, traffic, fire and bike-share provider modules