chore: ignore local agent workflows, commands, task notes, worktrees

Reserves .agents/, .claude/, .worktrees/, and _tasks/ for local-only
artefacts used by the /port-upstream-prs and /resolve-upstream-issues
slash commands. None of these paths should ever be tracked.

Author: diegosouzapw

.gitignore

@@ -6,3 +6,9 @@ dist/
 
 # WASM build output (built locally and in CI)
 ghostty-vt.wasm
+
+# Local-only agent workflows, commands, task notes and worktrees
+.agents/
+.claude/
+.worktrees/
+_tasks/