add-spikelisted

Flag a requirement as resting on an unvalidated technical assumption, so it can't be quietly implemented or marked done until a spike confirms it. $ARGUMENTS is the path to an HLD or LLD file, followed by either an existing `REQ-*` ID (optionally with a reason) or a freeform description of a new requirement to add already flagged. The path may be omitted if it's already clear from this conversation — see step 1. The REQ-ID or description is always required; if $ARGUMENTS has neither a path nor that, ask the user to provide it and stop. Steps: 1. Determine `<path>`: - If a path is present in $ARGUMENTS, use it. - If not, look back through this conversation for an HLD or LLD path already established (created via `/hld`/`/lld`, or referenced by an earlier `/spike`, `/add-spike`, `/resolve-open-questions`, `/implement-lld`, or `/reconcile` call in this session). If exactly one is found, confirm it with the user before proceeding rather than silently assuming. If more than one is found, list them and ask which to use. If none is found, ask the user to provide a path and stop. - Check that the file at `<path>` exists. If it does not, tell the user and stop. 1. Determine the target requirement: - If the remaining text starts with an existing `REQ-*` ID found in the doc's `## Requirements` section, that row is the target; anything after the ID is the reason/description of what's uncertain about it. - Otherwise, treat the remaining text as a freeform description of