[flowcool]

Problem

The current page depends on a generated full-page background. Text, gauges, thresholds, and values are then coupled to a raster asset, which makes generic maintenance and localization harder.

Change

• Keep a plant-only illustration as the static asset.
• Draw the title, subtitle, recommendation bands, gauges, needles, values, invalid-value placeholders, normal/inverted mode, maintenance, storage, and low-battery pages in ESPHome.
• Keep thresholds and scales fixed in YAML and retain the existing geometry and calculations.
• Add a generic reproduction example and preserve the existing generator and printable label metadata.

The contribution is generic. It contains no fleet inventory, Home Assistant access, MQTT threshold synchronization, NAS path, or device-specific calibration. HA alignment remains a manual YAML task.

Validation

• ESPHome 2026.10 isolated builds for API, MQTT, and standalone examples.
• Host renderer build and nine synthetic pixel cases, including normal/inverted, invalid values, range boundaries, long titles, and memory-sensitive layouts.
• Existing test suite plus the drawn-display tests.
• No energy claim is made; physical e-paper timing remains hardware dependent.

Refs #24