Move eterm emulation off the UI thread and add tabbed frontend

- introduce a per-terminal worker controller with ordered command queues,
    coalesced events, immutable snapshots, and deterministic shutdown
  - move PTY reads, parsing, history, selection, resize, reflow, and process
    status handling onto the terminal worker
  - publish terminal snapshots at the host refresh rate while preserving
    immediate idle, resize, interaction, and final-exit presentation
  - migrate TerminalDisplay, UITerminal, eterm, ecode, debugger, and ACP
    integrations away from direct mutable emulator access
  - synchronize scrollbar updates with acknowledged scroll commands
  - preserve title, clipboard, bell, prompt, color, restart, keep-alive,
    selection, input, and buffered process-exit behavior
  - add bounded synchronous selection requests and idempotent worker shutdown
  - make POSIX process launch safe after fork in multithreaded hosts and mark
    original PTY descriptors close-on-exec
  - add an UIApplication-based tabbed eterm with legacy CLI parity, tab
    lifecycle handling, close warnings, and default navigation shortcuts
  - add premake targets and deterministic controller, snapshot, lifecycle,
    concurrency, presentation, and exit-drain tests

src/tools/eterm/eterm.cpp

@@ -149,8 +149,7 @@ void inputCallback( InputEvent* event ) {
 }
 
 bool onCloseRequestCallback( EE::Window::Window* ) {
-	if ( warnBeforeClose &&
-		 Sys::processHasChildren( terminal->getTerminal()->getProcess()->pid() ) ) {
+	if ( warnBeforeClose && Sys::processHasChildren( terminal->getProcessId() ) ) {
 		displayingWarnBeforeClose = true;
 		needsRedraw = true;
 		return false;
@@ -366,7 +365,7 @@ EE_MAIN_FUNC int main( int argc, char* argv[] ) {
 		terminal->setFontHinting( fontHinting.Get() );
 		terminal->setFontAntialiasing( fontAntialiasing.Get() );
 
-		terminal->getTerminal()->setAllowMemoryTrimnming( true );
+		terminal->setAllowMemoryTrimming( true );
 		terminal->setCursorMode( cursorStyle.Get() );
 		terminal->pushEventCallback( [&closeOnExit]( const TerminalDisplay::Event& event ) {
 			if ( event.type == TerminalDisplay::EventType::TITLE ) {