[FEATURE] Dashboard v5: Historical analytics, data export, multi-sensor charts

[farcomiot]

📊 Dashboard v5 — Historical Analytics & Export

Parent: #1

Current State (v4.1)

• Live gauges for 11 sensors
• 24h chart history (from MQTT retained messages)
• Environmental health alerts (EPA/WHO thresholds)
• Noise event log with night watch

Proposed Features

• 7-day / 30-day history — extend SQLite queries via new MQTT topic
• Multi-sensor overlay charts — compare temp vs humidity, PM vs wind
• CSV/JSON export — download historical data for analysis
• Min/Max/Avg daily summary cards — aggregated daily stats
• Air Quality Index (AQI) — calculated from PM2.5 using EPA formula
• Trend arrows — visual indicator of rising/falling values
• Responsive mobile layout — optimized for phone screens
• PWA support — installable web app with offline indicator

Technical Approach

• Add MQTT topic farcom/enviro/history/7d for weekly aggregates
• Pi script publishes daily min/max/avg at midnight
• Dashboard fetches retained history messages on load
• Chart.js zoom plugin for time range selection

WordPress Constraints

• Zero blank lines (wpautop)
• No && operators (wptexturize)
• All tags in JS escaped as \x3c/\x3e
• Base64 chunk deployment pipeline

---

Ref: #1 Roadmap — Features