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/bt_locate.css

@@ -284,7 +284,7 @@
 #btLocateMap {
     position: absolute;
     inset: 0;
-    background: #1a1a2e;
+    background: var(--bg-primary, #07090e);
 }
 
 .btl-map-overlay-controls {
@@ -442,8 +442,8 @@
     text-transform: uppercase;
     letter-spacing: 0.5px;
     color: var(--accent-cyan, #00d4ff);
-    background: rgba(0, 212, 255, 0.1);
-    border: 1px solid rgba(0, 212, 255, 0.3);
+    background: rgba(var(--accent-cyan-rgb), 0.1);
+    border: 1px solid rgba(var(--accent-cyan-rgb), 0.3);
     border-radius: 4px;
     cursor: pointer;
     transition: all 0.2s;
@@ -452,7 +452,7 @@
 }
 
 .btl-detect-irk-btn:hover {
-    background: rgba(0, 212, 255, 0.2);
+    background: rgba(var(--accent-cyan-rgb), 0.2);
     border-color: var(--accent-cyan, #00d4ff);
 }