a11y + i18n: chat viewer filter placeholder + aria-label, status dot aria-hidden

Two unrelated small fixes bundled:

1. The chat viewer modal's filter input (chatViewerFilter) had a hardcoded "Filter..." placeholder that was never localized — every other filter input in the app routes its placeholder through UI_TEXT. Added queue.chatViewerFilterPlaceholder + queue.chatViewerFilterAria locale keys (DE: "Chat filtern..." / "Chatnachrichten filtern"; EN: "Filter chat..." / "Filter chat messages") and wired them through renderer-texts so the placeholder now matches the active language and screen readers get a proper accessible name on the input.

2. The status-bar's coloured dot (statusDot) had no aria-hidden — screen readers would read it as a generic element with no meaning. The status text right next to it already carries the same information ("Verbunden" / "Nicht verbunden"), so the dot is purely decorative. Added aria-hidden="true".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/index.html

@@ -802,7 +802,7 @@
 
             <div class="status-bar">
                 <div class="status-indicator">
-                    <div class="status-dot" id="statusDot"></div>
+                    <div class="status-dot" id="statusDot" aria-hidden="true"></div>
                     <span id="statusText">Nicht verbunden</span>
                 </div>
                 <span id="statusBarQueueSummary" class="status-bar-queue-summary"></span>