feat: menu de contexto em bottom sheet, painel de anexos, perfil e feed do mural

- Salas (chat, canais, murais e salas de espacos) abrem bottom sheet com grid de acoes
- Botao + da barra de digitacao abre painel de anexos em grid de 3 colunas que empurra a caixa de texto
- Modal do perfil permite editar nome/status e ler QR code (mobile)
- Alterar status atualiza localmente via extensao do SDK matrix
- Mural pre-carrega historico para exibir todas as midias em dispositivos sem cache

lib/pages/mural/mural_chat_page.dart

@@ -88,6 +88,7 @@ class _MuralChatViewState extends State<MuralChatView> {
   bool _descriptionExpanded = false;
   bool _loadingHistory = false;
   bool _historyEnded = false;
+  bool _initialLoading = false;
   final ScrollController _scrollController = ScrollController();
 
   @override
@@ -125,7 +126,8 @@ class _MuralChatViewState extends State<MuralChatView> {
     } catch (e, s) {
       Logs().w('Failed to load more mural posts', e, s);
     } finally {
-      if (timeline.events.length <= eventCountBefore) {
+      if (!timeline.canRequestHistory ||
+          timeline.events.length <= eventCountBefore) {
         _historyEnded = true;
       }
       _loadingHistory = false;
@@ -133,6 +135,25 @@ class _MuralChatViewState extends State<MuralChatView> {
     }
   }
 
+  /// Fetches older events from the server until enough media posts were
+  /// loaded or the entire history was consumed. This makes the mural behave
+  /// like a chat: after the initial sync only a handful of recent events are
+  /// in the timeline which usually contain very few media posts (most events
+  /// are thread comments), so we must actively fetch batches from the server
+  /// until the feed is properly populated.
+  Future<void> _fillInitialMedia() async {
+    var attempts = 0;
+    const maxAttempts = 20;
+    const targetMediaCount = 30;
+    while (mounted &&
+        !_historyEnded &&
+        _mediaEvents.length < targetMediaCount &&
+        attempts < maxAttempts) {
+      attempts++;
+      await _loadMore();
+    }
+  }
+
   void updateView() {
     if (!mounted) return;
     setState(() {});
@@ -142,12 +163,16 @@ class _MuralChatViewState extends State<MuralChatView> {
     timeline?.cancelSubscriptions();
     _loadingHistory = false;
     _historyEnded = false;
+    _initialLoading = true;
     timeline = await room.getTimeline(
       onUpdate: updateView,
       limit: Room.defaultHistoryCount * 3,
     );
     if (!mounted) return;
     setState(() {});
+    await _fillInitialMedia();
+    _initialLoading = false;
+    if (mounted) setState(() {});
   }
 
   Future<void> _sendFiles(List<XFile>? files) async {
@@ -318,7 +343,9 @@ class _MuralChatViewState extends State<MuralChatView> {
           ),
           const Divider(height: 1),
           Expanded(
-            child: events.isEmpty
+            child: _initialLoading
+                ? const Center(child: CircularProgressIndicator.adaptive())
+                : events.isEmpty
                 ? Center(
                     child: Padding(
                       padding: const EdgeInsets.all(24),