lazy backend boot and rename workspace to project

Backend isolate now boots in two phases: resolve toolchain on spawn
(binary availability only), initialize services on project.open. The
dispatcher stays empty until a project activates — IPC requests before
that return "No project active".

Scheduler ticker only runs while a project is open. Fires an immediate
first cycle on ProjectOpened so sidebar panels refresh without waiting
for the next interval. Stops on ProjectClosed.

Renamed workspace → project throughout backend messages
(project.validate, project.open, project.ready), callbacks
(onProjectOpen, onValidateProject), and methods
(openProject, validateProject, resolveProject).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/kernel/src/facade.dart

@@ -105,6 +105,8 @@ class KernelServices {
     DaemonClient? isolateClient,
     bool autoStartDaemonClient = true,
     Toolchain? toolchain,
+    Future<void> Function(String path)? onProjectOpen,
+    Future<String?> Function(String path)? onValidateProject,
   }) async {
     final log = Logger();
     final events = DaemonBus();
@@ -148,6 +150,8 @@ class KernelServices {
       events: events,
       settings: settings,
       toolchain: tc,
+      onProjectOpen: onProjectOpen,
+      onValidateProject: onValidateProject,
     );
     final ipc = isolateClient
         ?? (daemonClientFactory != null