0410 — Topic display identity stays two structured fields, not a concatenated name@vN string

Context. With versioned topics, log lines and metrics need to identify which physical topic they describe. A single combined string like orders@v2 is the common shorthand.

Decision. Every log line and metric carries "topic" (id or name) and "version" as separate structured fields; they are never concatenated.

Consequences. Filtering or aggregating by version alone works directly; a concatenated string would need parsing back apart anywhere that wants either half on its own.