fix(terminal): fix tabKey parsing for peerIds containing underscores (#14354)

Terminal tab keys use the format "peerId_terminalId". The previous code
used split('_')[0] or startsWith('$peerId_') to extract the peerId,
which breaks when the peerId itself contains underscores.

This can happen in two scenarios:
- Hostname-based ID: when OPTION_ALLOW_HOSTNAME_AS_ID is enabled, the
  peerId is derived from the system hostname, which commonly contains
  underscores (e.g. "my_dev_machine").
- Custom ID: the validation regex ^[a-zA-Z][\w-]{5,15}$ allows
  underscores since \w matches [a-zA-Z0-9_], so IDs like "my_dev_01"
  are valid.

Fix all three parsing sites in terminal_tab_page.dart to use
lastIndexOf('_'), which is safe because terminalId is always a plain
integer with no underscores.

flutter/lib/desktop/pages/terminal_tab_page.dart

@@ -194,7 +194,10 @@ class _TerminalTabPageState extends State<TerminalTabPage> {
         final currentTab = tabController.state.value.selectedTabInfo;
         assert(call.arguments is String,
             "Expected String arguments for kWindowEventActiveSession, got ${call.arguments.runtimeType}");
-        if (currentTab.key.startsWith(call.arguments)) {
+        // Use lastIndexOf to handle peerIds containing underscores
+        final lastUnderscore = currentTab.key.lastIndexOf('_');
+        if (lastUnderscore > 0 &&
+            currentTab.key.substring(0, lastUnderscore) == call.arguments) {
           windowOnTop(windowId());
           return true;
         }
@@ -329,7 +332,10 @@ class _TerminalTabPageState extends State<TerminalTabPage> {
   void _addNewTerminal(String peerId, {int? terminalId}) {
     // Find first tab for this peer to get connection parameters
     final firstTab = tabController.state.value.tabs.firstWhere(
-      (tab) => tab.key.startsWith('$peerId\_'),
+      (tab) {
+        final last = tab.key.lastIndexOf('_');
+        return last > 0 && tab.key.substring(0, last) == peerId;
+      },
     );
     if (firstTab.page is TerminalPage) {
       final page = firstTab.page as TerminalPage;
@@ -350,9 +356,10 @@ class _TerminalTabPageState extends State<TerminalTabPage> {
 
   void _addNewTerminalForCurrentPeer({int? terminalId}) {
     final currentTab = tabController.state.value.selectedTabInfo;
-    final parts = currentTab.key.split('_');
+    final tabKey = currentTab.key;
-    if (parts.isNotEmpty) {
+    final lastUnderscore = tabKey.lastIndexOf('_');
-      final peerId = parts[0];
+    if (lastUnderscore > 0) {
+      final peerId = tabKey.substring(0, lastUnderscore);
       _addNewTerminal(peerId, terminalId: terminalId);
     }
   }
@@ -369,9 +376,10 @@ class _TerminalTabPageState extends State<TerminalTabPage> {
           labelGetter: DesktopTab.tablabelGetter,
           tabMenuBuilder: (key) {
             // Extract peerId from tab key (format: "peerId_terminalId")
-            final parts = key.split('_');
+            // Use lastIndexOf to handle peerIds containing underscores
-            if (parts.isEmpty) return Container();
+            final lastUnderscore = key.lastIndexOf('_');
-            final peerId = parts[0];
+            if (lastUnderscore <= 0) return Container();
+            final peerId = key.substring(0, lastUnderscore);
             return _tabMenuBuilder(peerId, () {});
           },
         ));