[grafana] Template variables $chain and $instance have no default — all panels show No Data on fresh import

[obchain]

Refs #54

Location

deploy/grafana/charon.json — templating section ($chain, $instance variables)

Problem

Both $chain and $instance use label_values() which requires a live Prometheus data source with active metrics to populate. On fresh import (before the bot is running), both dropdowns are empty and every panel query filters on an empty label_values result, producing No Data across the entire dashboard.

If includeAll is false and no default value is set, operators must also manually select values from the dropdowns every time they open the dashboard after a bot restart that changes the instance label.

Impact

Poor operator experience on first import. The dashboard appears completely broken before confirming the setup is correct. For a tool intended as the primary observability interface, an empty dashboard on first open creates unnecessary confusion and erodes confidence in the tooling.

Suggested Fix

1. Set includeAll: true and current.value: $__all (or .*) for both $chain and $instance.
2. Set a hardcoded default for $chain (bsc or 56) since the project is BSC-only per CLAUDE.md v0.1 scope.
3. Add a dashboard description noting that variables auto-populate once the bot is running and Prometheus is scraping.

[obchain]

Fixed on feature branch; see feat/22-prometheus-metrics / feat/26-grafana-dashboard commits.