Three bugs fixed:
- NVS img_id now written before epd_init/draw; new draw_needed flag in NVS
survives power-loss mid-refresh so next boot re-draws from LittleFS instead
of showing stale content
- epd_sleep() now only called when display was initialized this cycle,
preventing a 60 s wait_busy() timeout on every 304 poll
- esp_task_wdt_reset() added to wait_busy() loop so the ~20 s 6-color
refresh no longer triggers the task watchdog
Also extracts normal_operation into operation.h template and adds
a native PlatformIO test suite (16 tests) covering the full response matrix.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
