feat(welcome): initialize a non-repo folder as a project (T-489)

Closes the new-project story (T-486). The dead-end "not a git repo" dialog now
offers to initialize the folder: project.init runs git init + a non-clobbering
scaffold, then opens + announces on projectCreatedChannel so the account
roadblock fires — the same path a brand-new project takes. Adds initExistingProject
+ the `clide project init [--dir]` verb (default: the current workspace).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/main.dart

@@ -340,6 +340,7 @@ Future<void> main() async {
       dispatcher,
       gitInit: (dir) => GitClient(toolchain: tc, workDir: Directory(dir)).init(),
       defaultParent: () => workRoot.parent.path,
+      defaultInitPath: () => workRoot.path,
     );
     final pql = PqlClient(workDir: workRoot, toolchain: tc);
     registerPqlCommands(dispatcher, pql);