The flow vitals carry gate minutes and the red-batch rate, and a rate over 30% is named as a miss #6428

Flow work for #5930. It joins the two reads into the one vitals reading, after #6424 has added the other new fields, so the two never edit Vitals at once.

Done when:

• [ ] Vitals gains gateMinutes1h, pullCheckMinutes1h and redBatchRate, filled by readGateMinutes and readRedBatches with the same publicOnly.
• [ ] vitalsMisses adds "N% of merge batches went red in 6 h" when the rate is over 0.3 and at least 3 batches finished.
• [ ] Home's flow line, the tick line and MCP flow show them, as #6424 does for its fields.
• [ ] Tests cover the miss's thresholds (0.3 and the minimum of 3) and the new fields.

Files: src/flow/vitals.ts and the readers #6424 touches, test/flow-vitals*.test.ts.