fix: apply getVisibleSessions filter in renderSheetList for mobile bottom sheet

Hidden sessions were still appearing in the mobile bottom-sheet session
switcher because renderSheetList() read _currentSessions directly,
bypassing the getVisibleSessions() helper used by renderGrid() and
renderSidebar().

- app.js: sortByPriority now receives getVisibleSessions(_currentSessions)
  instead of _currentSessions directly in renderSheetList()
- test_frontend_js.py: add test_render_sheet_list_filters_hidden_sessions
  to assert getVisibleSessions is called in renderSheetList body

Completes consistent hidden-sessions filtering across all three render
paths (grid, sidebar, mobile bottom sheet).

Co-authored-by: Amplifier <amplifier@amplified.dev>

muxplex/frontend/app.js

@@ -1261,7 +1261,7 @@ function closeBottomSheet() {
 function renderSheetList() {
   var list = $('sheet-list');
   if (!list) return;
-  var sorted = sortByPriority(_currentSessions);
+  var sorted = sortByPriority(getVisibleSessions(_currentSessions));
   list.innerHTML = sorted.map(function(s) {
     var hasBell = s.bell && s.bell.unseen_count > 0 &&
       (s.bell.seen_at === null || s.bell.last_fired_at > s.bell.seen_at);

muxplex/tests/test_frontend_js.py

@@ -2263,6 +2263,24 @@ def test_render_sidebar_uses_visible_array() -> None:
     )
 
 
+# ── app.js: renderSheetList filters hidden sessions ───────────────────────────
+
+
+def test_render_sheet_list_filters_hidden_sessions() -> None:
+    """renderSheetList() must filter out hidden sessions via getVisibleSessions()."""
+    match = re.search(
+        r"function renderSheetList\s*\(\)\s*\{(.*?)(?=\n(?:function|//|window\.))",
+        _JS,
+        re.DOTALL,
+    )
+    assert match, "renderSheetList function not found in app.js"
+    body = match.group(1)
+    assert "getVisibleSessions" in body, (
+        "renderSheetList must call getVisibleSessions() to filter hidden sessions; "
+        "currently it reads _currentSessions directly and bypasses the filter"
+    )
+
+
 # ── app.js: DOMContentLoaded calls loadServerSettings ────────────────────────