[fix](trx-frontend-http): use dedicated --ais-accent color for map markers

Replace --accent-red with a new --ais-accent CSS variable (default #00aacc
cyan-blue) so AIS vessel markers and track lines are visually distinct from
other UI elements regardless of theme. Light theme uses a slightly darker
#0088aa for readability on the map.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/style.css

@@ -12,6 +12,7 @@
   --accent-green: #c24b1a;
   --accent-yellow: #f0ad4e;
   --accent-red: #e55353;
+  --ais-accent: #00aacc;
   --control-height: 2.6rem;
   --jog-hi: #243a5b;
   --jog-lo: #14233a;
@@ -46,6 +47,7 @@
   --accent-green: #b04317;
   --accent-yellow: #b57600;
   --accent-red: #cf3f3f;
+  --ais-accent: #0088aa;
   --jog-hi: #e6edf8;
   --jog-lo: #cdd9eb;
   --jog-shadow: rgba(58, 79, 110, 0.18);