refactor(monitoring): rearchitect taupi-fan dashboard & clean up docs
Dashboard changes:
- Merge 3 separate correlation graphs into one full-width panel
- Left Y axis: temperatures + dewpoints (°C)
- Right Y axis: humidity + mold threshold (%)
- Boolean signals (fan/mold/activation) as colored fill bands
- graphTooltip: 2 for shared crosshair + tooltip
- Add collapsed Deep Dive row with delta graphs
- Collapse BLE diagnostics row
Documentation changes:
- DASHBOARD_CREATION.md: remove content now covered by Grafana skills
(dashboarding, grafana-oss, promql), eliminate duplicated pitfalls
section, add Prometheus dashboard guidance, add Grafana unit codes
- AGENTS.md: add skills prerequisite table, update folder structure
(add taupi-fan.yaml), add Prometheus data flow, remove duplicated
InfluxDB/Flux/pitfalls sections (canonical in DASHBOARD_CREATION.md)
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