Grafana dashboard: cover the full metric set and ship a shareable export

[Pixnop]

Feedback from Th3Dilli after running the stack against a real server: the provisioned dashboard reads as WIP, plenty of families have no panel, and there is no way to hand the dashboard to someone outside the provisioning setup. Two asks in one deliverable:

• Panels for the families the dashboard skips today: engine busy time, network rates and totals, suspend windows, entities by code, engine warnings by kind, deaths, ping, uptime, worldgen and the runtime set.
• A second JSON in export-for-sharing form: datasource as an __inputs variable so Grafana's import dialog asks which Prometheus to bind, instead of the provisioning file's hardwired datasource. The provisioned variant stays as is; the shared one is what gets linked from the README.

The metric families and their meanings are all in the main README.

[Pixnop]

Done in #46 (plus the gate follow-ups #47-#49): 41 panels covering every family, and contrib/grafana/pulse-overview-shared.json imports through Grafana's dialog with a datasource prompt. The shared file is generated from the provisioned one by make-shared.py.