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.

changelog.d/1172-cctv-missing-numbers.md

@@ -0,0 +1,13 @@
+- Keep missing CCTV numbers unknown instead of reading them as zero. `Number`
+  turns null, blank strings and booleans into 0 or 1, and the camera source
+  list sends an unknown number as JSON null, so a source-pack camera that left
+  out its pose reached the browser as zeros clamped to each field's floor —
+  facing north, pitch −2°, FOV 20°, range 120 m, mount 6 m and ground 0 m —
+  instead of the defaults (id-hash heading, −17°, 74°, 700 m, 24 m and the
+  city's ground); a null or blank position placed the camera at 0,0. The
+  server's `toFiniteNumber` and the browser's `safeNumber` now treat absent,
+  blank and boolean values as missing. The same conversion also stops a
+  Tallinn row with a null heading reading as a confident north-facing camera,
+  a Caltrans camera with a blank elevation losing its 150 m ground prior, and
+  a TfL or Catalonia camera with a null or blank coordinate being kept at 0,0
+  or on the zero meridian (omerbberk, #1172).