feat(runtime): lazy runtime-manifest for volatile config + activation metric

Externalize 8 upstream base URL(s) + citation-grammar version into
br-runtime.json.gz pulled from this repo's GitHub Release on first tool call.
Repoint a dead endpoint via runtime/br-runtime.json + release workflow WITHOUT a
PyPI release; falls back to the hardcoded client defaults (offline-safe). The unlinked
asset's download_count is a per-connector activation metric. Fleet rollout of the
de-eli-mcp pilot (matematicsolutions/de-eli-mcp#2).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>