openspec-continue-change

Continue working on a change by creating the next artifact. **Store selection:** If the user names a store (a store is a standalone OpenSpec repo registered on this machine) or the work lives in one, run `openspec store list --json` to discover registered store ids, then pass `--store <id>` on the commands that read or write specs and changes (`new change`, `status`, `instructions`, `list`, `show`, `validate`, `archive`, `doctor`, `context`). Other commands do not take the flag. Hints printed by commands already carry the flag; keep it on follow-ups. Without a store, commands act on the nearest local `openspec/` root. **Input**: Optionally specify a change name. If omitted, check if it can be inferred from conversation context. If vague or ambiguous you MUST prompt for available changes. **Steps** 1. **If no change name provided, prompt for selection** Run `openspec list --json` to get available changes sorted by most recently modified. Then use the **AskUserQuestion tool** to let the user select which change to work on. Present the top 3-4 most recently modified changes as options, showing: - Change name - Schema (from `schema` field if present, otherwise "spec-driven") - Status (e.g., "0/5 tasks", "complete", "no tasks") - How recently it was modified (from `lastModified` field) Mark the most recently modified change as "(Recommended)" since it's likely what the user wants to continue. **IMPORTANT**: Do NOT guess or auto-select a change. Alwa...