picker-first startup with per-project sticky override (T-115)

Boot used to auto-open app.lastProject and fall back to the CWD; new
default is the welcome screen as the project picker. Sticky-open is
opt-in: a checkbox on each recent-projects row toggles a
startupSticky flag, and clide auto-opens iff exactly one row has it.
Two-or-more, or none, ⇒ picker (unambiguous user intent).

RecentProject gains the boolean (persisted in app.recentProjects);
ProjectManager exposes stickyProjectPath, openStickyOrNothing,
setStickyStartup, isStickyStartup, and preserves the flag across
reopens.

Co-Authored-By: Claude <noreply@anthropic.com>

lib/main.dart

@@ -156,10 +156,10 @@ Future<void> main() async {
 
   if (!kIsWeb) {
     await services.project.loadRecents();
-    var opened = await services.project.openLast();
-    if (!opened) {
-      opened = await services.project.open(Directory.current.path);
-    }
+    // T-115: picker-first. Auto-open only when exactly one recent has
+    // its sticky-startup flag set; otherwise the welcome tab (default
+    // workspace content) serves as the project picker.
+    final opened = await services.project.openStickyOrNothing();
     if (opened) {
       services.panels.activateTab(Slots.workspace, 'claude.primary');
     }