Replace +/- disclosure indicators with a rotating chevron in RoomInfoPanel

The Files/Integrations/Room settings section toggles used a trailing
"+"/"-" glyph -- confusing as a collapse/expand affordance. Replaced with
a small chevron placed before the label, pointing right when collapsed
and rotating 90deg clockwise (pointing down) when expanded, the more
conventional disclosure-triangle pattern.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/components/RoomInfoPanel.css

@@ -193,6 +193,9 @@
 }
 
 .room-info-settings-toggle {
+  display: flex;
+  align-items: center;
+  gap: 6px;
   background: transparent;
   border: 1px solid var(--ds-border);
   color: var(--ds-text);
@@ -205,6 +208,17 @@
   text-align: left;
 }
 
+.room-info-settings-chevron {
+  display: inline-flex;
+  flex: none;
+  color: var(--ds-muted);
+  transition: transform 0.15s ease;
+}
+
+.room-info-settings-chevron-open {
+  transform: rotate(90deg);
+}
+
 .room-info-settings-form {
   display: flex;
   flex-direction: column;