## Problem
Previous versions would clear WiFi credentials on connection failure,
requiring manual reconfiguration via captive portal after each WiFi outage.
## Solution
- Never clear credentials on connection failure
- Infinite retry with exponential backoff (5s → 10s → 20s → ... → 5min max)
- Fallback AP ("TJ56654-Setup") enabled after ~5 min of failed attempts
- Dual STA+AP mode allows configuration while still retrying connection
- AP automatically disabled when WiFi reconnects
## Changes
### WiFi Credential Handling
- Try SDK-stored credentials first (from WiFiManager)
- Fall back to EEPROM config if SDK credentials fail
- Fixes OTA update credential loss issue
### User Experience
- Display shows "No WiFi" with retry countdown instead of cryptic numbers
- "!" indicator in date line when WiFi is disconnected
- Clock continues running with last synced time during outage
### Network Activity (~50 requests/day)
| Service | Interval | Endpoint |
|---------|----------|----------|
| NTP | 1 hour | pool.ntp.org:123 (UDP) |
| Weather | 30 min | api.open-meteo.com (HTTP) |
| mDNS | continuous | 224.0.0.251 (multicast) |
Co-authored-by: Alex Petrochenko <petrochenko@life-pay.ru>
