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>

app.py

@@ -209,7 +209,7 @@ def inject_offline_settings():
             "enabled": get_setting("offline.enabled", False),
             "assets_source": assets_source,
             "fonts_source": fonts_source,
-            "tile_provider": get_setting("offline.tile_provider", "cartodb_dark_cyan"),
+            "tile_provider": get_setting("offline.tile_provider", "cartodb_dark_nolabels"),
             "tile_server_url": get_setting("offline.tile_server_url", ""),
         }
     }
@@ -440,8 +440,8 @@ def get_sdr_device_status() -> dict[str, str]:
 @app.before_request
 def require_login():
     # Skip auth entirely when INTERCEPT_DISABLE_AUTH is set
-    if os.environ.get('INTERCEPT_DISABLE_AUTH', '').lower() in ('1', 'true', 'yes'):
-        session['logged_in'] = True
+    if os.environ.get("INTERCEPT_DISABLE_AUTH", "").lower() in ("1", "true", "yes"):
+        session["logged_in"] = True
         return None
 
     # Routes that don't require login (to avoid infinite redirect loop)