feat(files): treat in-repo .worktrees/ checkouts as ignored (T-511)

D-106 supports opening a worktree under <repo>/.worktrees/ as its own
workspace; the dir itself is sibling checkouts, not tree content — so
the builtin ignore set hides it and the project-init scaffold
gitignores it alongside .clide/.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/src/daemon/project_commands.dart

@@ -84,7 +84,7 @@ void _writeScaffold(String dir, String name) {
   // Claude with an empty CLAUDE.md stub. No language/framework templates. Never
   // clobbers — safe to run over an existing folder (T-489).
   final gitignore = File('$dir/.gitignore');
-  if (!gitignore.existsSync()) gitignore.writeAsStringSync('# clide\n.clide/\n');
+  if (!gitignore.existsSync()) gitignore.writeAsStringSync('# clide\n.clide/\n.worktrees/\n');
   final claudeMd = File('$dir/CLAUDE.md');
   if (!claudeMd.existsSync()) claudeMd.writeAsStringSync('# $name\n\nGuidance for Claude Code in this project.\n');
 }

lib/src/files/ignore.dart

@@ -162,5 +162,7 @@ class IgnoreSet {
   /// ignore files. Matches D-004's "walker magic: none except
   /// `.git/`" — but the tree-view UI benefits from hiding `.pql/` and
   /// `.dart_tool/` too since users never edit those by hand.
-  static IgnoreSet builtin() => IgnoreSet.parse(const ['.git/\n.pql/\n.clide/\n.dart_tool/\nbuild/\nnode_modules/\n']);
+  /// `.worktrees/` holds in-repo linked worktrees (D-106) — sibling
+  /// checkouts a user opens as their own workspaces, not tree content.
+  static IgnoreSet builtin() => IgnoreSet.parse(const ['.git/\n.pql/\n.clide/\n.dart_tool/\n.worktrees/\nbuild/\nnode_modules/\n']);
 }