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>

templates/login.html

@@ -12,6 +12,8 @@
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <title>iNTERCEPT // Restricted Access</title>
     <script src="{{ url_for('static', filename='js/core/login.js') }}"></script>
+    <link rel="stylesheet" href="{{ url_for('static', filename='css/fonts-local.css') }}" />
+    <link href="https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&family=JetBrains+Mono:wght@400;500;600;700&family=Roboto+Condensed:wght@300;400;500;600;700&display=swap" rel="stylesheet">
     <link rel="stylesheet" href="{{ url_for('static', filename='css/index.css') }}" />
     <link rel="stylesheet" href="{{ url_for('static', filename='css/login.css') }}" />
   </head>