builds board: a Grafana dashboard of the container builds, from the lines hive-c0re logs

A builds tab (counts, failures, longest, builds over time by outcome, a table of
each build) and an output tab (every line of the build picked in the Build
filter). The table joins its grouped stats by labels, one row per build.

docs/swarm/services.md

@@ -204,6 +204,7 @@ kept.
 - `authelia`, `bao`, `queue`: the identity provider, the secret store and the NATS queue.
 - `claude-usage`: Claude use by model, effort, token type and source. Filter by hive, service (agents or the review classifier) and agent. The service filter separates the classifier's API-key spend from the agents.
 - `egress`: what agents send through the egress proxy, in three tabs. **overview** has the totals (requests, agents active, refused, credential challenges, data transferred), requests over time by status, and the busiest agents and destinations. **refused** lists the hosts the proxy refused for each agent. **would-deny** lists what agents in `log` mode reached that restricted mode would refuse. The host lists are tables, one row per host (and agent), with a count column you can sort. Filter by agent.
+- `builds`: the container builds hive-c0re ran on every hive, in two tabs. **builds** has the count, the failures and the longest, builds over time by outcome, and a table of each build with its id, agent, kind, outcome and runtime. **output** shows every line of the build picked in the **Build** filter, with its start and finish lines. It reads the lines hive-c0re logs for each build, so a hive-c0re that doesn't log them leaves it empty. Filter by agent.
 - `controller`: the swarm controller's job graph by state, and the push and commit rates it sees on the forge.
 - `review-classifier`: review requests by outcome, the verdict mix, results per check, retried asks, and run duration p50 and p95.
 - `forge`: what the forge holds, and the forge process's CPU, memory and descriptors.