Thin local front-end over ANW-26's merge engine (query::execute_merge):
walk the vault once (vault::scan, same as doctor), evaluate the --query
string, assemble the merged document, write it to stdout. No HTTP, no
watcher, no index. Byte-identical to the HTTP merge mode for the same
vault and query.
Accept: text/markdown on /query concatenates matched note bodies into one
markdown document, each fragment preceded by an HTML-comment source marker.
Adds __anw-order (frontmatter-key ordering, asc/desc, missing-key-last) and
__anw-kind (homogeneity guard, 400 on a mixed merge). Both evaluate over the
full matched set before __anw-limit truncates. Merge mode uses its own
body-cloning projection; the JSON path is unchanged (no body clone).
