fix: treat AIS "not available" speed and course as unknown

ITU-R M.1371 encodes speed over ground in 0.1-knot units and course over
ground in 0.1-degree units, reserving the top code of each field for "not
available": SOG 1023 reaches us as 102.3 knots and COG 3600 as 360 degrees.
Both are finite, so numberValue passed them through as ordinary readings and
every consumer — vessel cards, the HUD, voice analyst queries — treated a
missing measurement as a real one.

Observed on a live AISStream feed of 3,062 vessels: exactly 3 records at
102.3 knots with no reading anywhere between 40 and 102.3, and 404 records
at exactly 360 degrees. One Dutch rescue boat moored at its station carried
both sentinels at once, so an analyst summary reported a maximum speed of
102.3 knots — faster than any vessel afloat.

Filter both at the store, where AISStream messages are decoded, so the
sentinels never enter the cache. Heading already had this treatment through
normalizedHeading with its own separate sentinel of 511.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

server/providers/vessels/ais-store.js

@@ -72,8 +72,8 @@ export function ingestAisStreamEnvelope(envelope) {
     imo: stringValue(message.ImoNumber ?? message.IMO ?? staticData.imo),
     type: vesselTypeFromAis(message, staticData),
     destination: stringValue(message.Destination ?? staticData.destination),
-    speed: numberValue(message.Sog ?? message.SOG),
-    course: numberValue(message.Cog ?? message.COG),
+    speed: normalizedSpeedOverGround(message.Sog ?? message.SOG),
+    course: normalizedCourseOverGround(message.Cog ?? message.COG),
     heading: normalizedHeading(message.TrueHeading ?? message.Heading),
     last_position_UTC: normalizeAisTimestamp(
       metadata.time_utc ?? metadata.TimeUtc,
@@ -277,6 +277,28 @@ function normalizedHeading(value) {
   return heading !== null && heading >= 0 && heading <= 360 ? heading : null;
 }
 
+/**
+ * Speed over ground in knots, or null when the report carries AIS's "not
+ * available" code. ITU-R M.1371 encodes SOG in 0.1-knot units where 1022 means
+ * "102.2 knots or higher" and 1023 means unavailable, so 102.3 is a sentinel
+ * and not a reading. It is finite, so every consumer would otherwise treat it
+ * as a genuine speed.
+ */
+function normalizedSpeedOverGround(value) {
+  const speed = numberValue(value);
+  return speed !== null && speed >= 0 && speed < 102.3 ? speed : null;
+}
+
+/**
+ * Course over ground in degrees, or null when the report carries AIS's "not
+ * available" code (3600 in 0.1-degree units, i.e. 360). Valid courses stop at
+ * 359.9; heading keeps its own separate sentinel of 511.
+ */
+function normalizedCourseOverGround(value) {
+  const course = numberValue(value);
+  return course !== null && course >= 0 && course < 360 ? course : null;
+}
+
 function normalizeAisTimestamp(value) {
   const text = stringValue(value);
   if (!text) return new Date().toISOString();