v4.0.1: Fix truncated MQTT topics

v4.0.1: Fix truncated MQTT topics

Bug-fix release for ESP8266 and ESP32. MQTT topics saved in display profiles now support up to 127 UTF-8 bytes. Previously, they were silently cut to 31 bytes, so longer topics stopped receiving messages after saving or applying a profile.

Fixed

• Expanded profile MQTT topics from 31 to 127 bytes.
• Expanded all three progress-bar source IDs from 47 to 127 bytes, covering regular data, conditions and dynamic animation sources for MQTT and HA.
• Added length validation to the profile editor, configuration APIs and backup restore. Overlong values are rejected instead of silently truncated; the editor keeps the entered text so it can be corrected.
• Added a hint for profile topics that may have been truncated by older firmware.
• Preserved existing profiles and progress-bar settings through migration of older raw and compressed storage records on both platforms.

Updating

1. Download and keep a private settings backup before updating.
2. Install wledPixel-v4.0.1_ESP8266.bin or wledPixel-v4.0.1_ESP32.bin for your board through the firmware-update page. These are application images, not merged ESP32 factory images. Check the download against SHA256SUMS.
3. Confirm v4.0.1 after reboot. If a topic was already truncated, enter its full value again and save the profile. Missing characters cannot be recovered from the stored prefix.

Existing v4.0 and beta profiles and settings backups remain supported. The backup JSON format is unchanged. Keep a backup made with the older firmware if you need to downgrade: install that firmware and restore its matching backup.

Validation

• Native C++ tests with AddressSanitizer and UndefinedBehaviorSanitizer cover the reported topic, the 127-byte boundary, ASCII/UTF-8 overflow rejection, old-record migration, storage round trips and interrupted writes.
• Python and JavaScript tests check byte-length validation, web assets, OTA guards and backup comparison. Normal and HIL builds pass for both platforms; only normal firmware images are distributed.
• The fix was tested on physical ESP8266 and ESP32 devices: full topics survived saving, backup export and reboot, and real messages on 127-byte MQTT topics reached data, condition and dynamic animation sources. Original settings were restored and compared with their backups after testing.

All other v4.0 features remain available; see the v4.0 release notes for the full overview.