chore: ignore go.work local workspace

When building the gomobile binding from a git worktree outside the registry
tree, pkg/client's replace to fn-registry needs an absolute path. A local
go.work (gitignored) supplies it without touching the committed go.mod.

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

.gitignore

@@ -14,3 +14,7 @@ worker.id
 /chat
 *.exe
 registry.db
+
+# local workspace (no committear: replace absoluto al registry)
+go.work
+go.work.sum