fix: resolve new tab creation failure and shortcut passthrough

- Fix pty.spawn cwd tilde expansion: ptyManager now passes resolvedCwd (expanding ~ and verifying directory existence) so child processes do not exit immediately on launch
- Add pointer-events: none to SVGs inside buttons and tabs to prevent Electron window-dragging interception
- Extend xterm attachCustomKeyEventHandler to allow Ctrl+Shift+T, Ctrl+Shift+W, etc. through while terminal is focused
- Wrap remote SSH and serial spawns with fallback to local bash to prevent tab death loops on connection failures

src/renderer/css/app.css

@@ -100,6 +100,11 @@ body {
   flex-shrink: 0;
 }
 
+.btn-icon svg,
+.btn-icon svg * {
+  pointer-events: none !important;
+}
+
 .btn-icon:hover {
   background: var(--btn-hover, rgba(255, 255, 255, 0.08));
   color: var(--text-bright);
@@ -115,7 +120,7 @@ body {
   align-items: center;
   gap: 2px;
   margin-left: 6px;
-  -webkit-app-region: no-drag;
+  -webkit-app-region: no-drag !important;
 }
 
 .win-btn {
@@ -130,6 +135,12 @@ body {
   justify-content: center;
   cursor: pointer;
   transition: all 0.15s ease;
+  -webkit-app-region: no-drag !important;
+}
+
+.win-btn svg,
+.win-btn svg * {
+  pointer-events: none !important;
 }
 
 .win-btn:hover {