Add Docker Compose observability stack for Lightbringer

[NeerajGodiyal]

Summary:

• Add Docker Compose services for InfluxDB, Grafana, and optional Lightbringer runtime.
• Provision the four Lightbringer dashboards and harden startup with readable-input preflight checks.
• Remove the tracked direnv helper with a user-specific absolute path.

Verification:

• git diff --check
• jq empty docker/grafana/dashboards/*.json
• YAML parse for compose/provisioning files
• shellcheck docker/secrets/check-readable.sh docker/influxdb/init-database.sh docker/grafana/entrypoint.sh
• cargo fmt --check
• Docker Compose config/preflight checks on Linux server
• Live Lightbringer + InfluxDB + Grafana smoke test with fresh completion, repair, and memory data