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/js/modes/waterfall.js

@@ -3014,10 +3014,14 @@ const Waterfall = (function () {
         }
 
         // Backend stop is fire-and-forget; UI is already updated above.
+        const _audioStopCtrl = new AbortController();
+        const _audioStopTid = setTimeout(() => _audioStopCtrl.abort(), 3000);
         try {
-            await fetch('/receiver/audio/stop', { method: 'POST' });
+            await fetch('/receiver/audio/stop', { method: 'POST', signal: _audioStopCtrl.signal });
         } catch (_) {
             // Ignore backend stop errors
+        } finally {
+            clearTimeout(_audioStopTid);
         }
 
         if (resumeWaterfall && _active) {
@@ -3222,10 +3226,14 @@ const Waterfall = (function () {
 
         if (_es) {
             _closeSseStream();
+            const _wfStopCtrl = new AbortController();
+            const _wfStopTid = setTimeout(() => _wfStopCtrl.abort(), 3000);
             try {
-                await fetch('/receiver/waterfall/stop', { method: 'POST' });
+                await fetch('/receiver/waterfall/stop', { method: 'POST', signal: _wfStopCtrl.signal });
             } catch (_) {
                 // Ignore fallback stop errors.
+            } finally {
+                clearTimeout(_wfStopTid);
             }
         }