Openspec Sync Specs

This syncs delta specs from an openspec change back into your main specs without archiving the change. It reads the delta files (which mark requirements as ADDED, MODIFIED, REMOVED, or RENAMED) and intelligently merges them into your main spec files. The key bit is that it does smart merging instead of blind replacement, so you can add a single scenario to an existing requirement without copying everything else over. It prompts you to pick which change to sync if you don't specify one, then walks through each capability's delta and applies the changes. Useful when you want to keep a change branch active but pull its spec updates into main as you go.