Optional OTLP export of request-level metrics (request and response-byte
counters keyed by route/status/conditional-GET, a duration histogram out
to 600s) plus server spans for slow or 5xx requests, nested under the
incoming W3C trace context. Off unless an OTLP endpoint or uptrace DSN is
configured; a config-less server is byte-for-byte unchanged.
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).
