feat: expand manual-placeholder support for unsupported dashboard widgets

## Summary
Post-release capability backlog for widgets/query shapes that migrated as manual or not-feasible placeholders in the release dashboard batch.

## Examples from the batch
Grafana:
- RabbitMQ vector-matching joins: `Log entries committed / s`, `Leader elections / s`.
- Envoy histogram/label_replace gaps.
- JVM divergent arithmetic/grouping in `GC Pressure`.

Datadog:
- Status/manage widgets that need Elastic Synthetics or alert-rule equivalents.
- `event_stream`, `hostmap`, `topology_map`.
- Logs pattern streams and security_signals source panels.
- Vault `ewma_3` formula in `Login request latency`.

## Acceptance criteria
- Each unsupported class either gains translator support or has a documented, user-actionable manual migration recipe.
- Coverage matrix is updated when support is added.

Start by inventorying translator support and the coverage matrix for the listed Grafana and Datadog widget and query classes. Done means each unsupported class either has translator support or a documented, user-actionable manual migration recipe, with the coverage matrix updated.

Written by the indexing model from the issue text.