fix(cctv): keep missing numbers unknown instead of reading them as zero

Number() reads null, blank strings and booleans as 0 (or 1), and
/api/cctv/sources sends an unknown number as JSON null. A source-pack
camera that left out its pose therefore reached the browser as zeros
clamped to each field's floor (north, pitch -2, FOV 20, range 120 m,
mount 6 m, ground 0 m) instead of taking the defaults, and a null or
blank position put the camera at 0,0.

toFiniteNumber (server) and safeNumber (browser) now return the fallback
for absent, blank and boolean values, as validateBox already does for
Recent Imagery. The same conversion fixes the per-pack paths: a Tallinn
row with a null heading no longer reads as a high-confidence north-facing
camera, a Caltrans camera with a blank elevation keeps its 150 m ground
prior, and TfL or Catalonia cameras with a null or blank coordinate are
dropped instead of kept at 0,0 or on the zero meridian.

server/providers/cctv/normalize.js

@@ -39,11 +39,21 @@ export function escapeXml(text) {
 /**
  * Coerce a value to a finite number, returning fallback if NaN/Infinity.
  *
+ * Absent, blank and boolean values take the fallback too: `Number` reads
+ * null, '' and false as 0, which would turn a missing coordinate, heading or
+ * elevation into a real zero.
+ *
  * @param {*} value
  * @param {number} [fallback=NaN]
  * @returns {number}
  */
 export function toFiniteNumber(value, fallback = NaN) {
+  if (
+    value == null ||
+    typeof value === 'boolean' ||
+    (typeof value === 'string' && !value.trim())
+  )
+    return fallback;
   const num = Number(value);
   return Number.isFinite(num) ? num : fallback;
 }