fix: resolve two-window hang and sweep UI/theming updates

Fix app becoming unresponsive when two browser windows are open: the
root cause was HTTP/1.1 connection pool exhaustion (6-connection limit
per origin). VoiceAlerts was opening 3 SSE streams per window by
default, so two windows produced 8 connections and permanently starved
all regular HTTP requests.

- voice-alerts.js: default all streams to false (opt-in) to stay within
  the browser connection limit; existing user preferences in localStorage
  are preserved
- routes/alerts.py: replace direct AlertManager.stream_events() with
  sse_stream_fanout so both windows receive every alert instead of
  competing for the same queue
- routes/bluetooth_v2.py: same fanout fix via subscribe_fanout_queue,
  preserving named SSE events (device_update, scan_started, etc.)

Also includes accumulated UI/theming changes: accent-cyan CSS variable
sweep across mode CSS/JS files, standalone dashboard pages, template
updates, satellite TLE data refresh, and tile provider default rename.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

static/css/modes/morse.css

@@ -199,3 +199,17 @@
         align-items: stretch;
     }
 }
+
+html[data-ui-tier="enhanced"] .morse-raw-panel {
+    border-color: rgba(46, 125, 138, 0.18);
+    background: rgba(1, 4, 4, 0.9);
+}
+
+html[data-ui-tier="enhanced"] .morse-raw-text {
+    color: rgba(70, 180, 200, 0.90);
+}
+
+html[data-ui-tier="enhanced"] .morse-metrics-panel span {
+    border-color: rgba(46, 125, 138, 0.18);
+    background: rgba(1, 4, 4, 0.88);
+}