gsd-ns-ideate

Route to the appropriate exploration / capture skill based on the user's intent. `gsd-note`, `gsd-add-todo`, `gsd-add-backlog`, and `gsd-plant-seed` were folded into `gsd-capture` (with `--note`, default, `--backlog`, `--seed` modes) by #2790. The capture target lists pending todos via `--list`. | User wants | Invoke | |---|---| | Explore an idea or opportunity | gsd-explore | | Sketch out a rough design or plan | gsd-sketch | | Time-boxed technical spike | gsd-spike | | Write a spec for a phase | gsd-spec-phase | | Capture a thought (todo / note / backlog / seed) | gsd-capture | Invoke the matched skill directly using the Skill tool.