Fix UI review issues: accessibility, i18n, duplicate IDs, URL overflow

- Rename duplicate id="settings-error" to "device-settings-error"
- Add missing i18n key value_source.scene_sensitivity.hint (en/ru/zh)
- Add accessible label to password-toggle and Stop All buttons
- Add aria-hidden toggle on connection overlay
- Fix static image URL overflow with ellipsis truncation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/locales/en.json

@@ -25,6 +25,7 @@
   "auth.logout.success": "Logged out successfully",
   "auth.please_login": "Please login to view",
   "auth.session_expired": "Your session has expired or the API key is invalid. Please login again.",
+  "auth.toggle_password": "Toggle password visibility",
   "displays.title": "Available Displays",
   "displays.layout": "Displays",
   "displays.information": "Display Information",
@@ -1162,6 +1163,7 @@
   "value_source.auto_gain.enable": "Enable auto-gain",
   "value_source.sensitivity": "Sensitivity:",
   "value_source.sensitivity.hint": "Gain multiplier for the audio signal (higher = more reactive)",
+  "value_source.scene_sensitivity.hint": "Gain multiplier for the luminance signal (higher = more reactive to brightness changes)",
   "value_source.smoothing": "Smoothing:",
   "value_source.smoothing.hint": "Temporal smoothing (0 = instant response, 1 = very smooth/slow)",
   "value_source.audio_min_value": "Min Value:",
@@ -1309,6 +1311,7 @@
   "target.error.stop_failed": "Failed to stop target",
   "target.error.clone_failed": "Failed to clone target",
   "target.error.delete_failed": "Failed to delete target",
+  "targets.stop_all.button": "Stop All",
   "targets.stop_all.none_running": "No targets are currently running",
   "targets.stop_all.stopped": "Stopped {count} target(s)",
   "targets.stop_all.error": "Failed to stop targets",