web-installer: FP6: flash AB images to both slots

Description

Flash following images to both slots to address issue where image on inactive slot has higher spl:
boot dtbo vbmeta_system vbmeta init_boot pvmfw recovery vendor_boot

Screenshots

Technical details

Tests

• Flash FPOS version N-1: Currently VS1E
• OTA to FPOS version N -> Currently FP6.QREL.15.148.0.20250913182929_VS1O
• Flash /e/OS through web installer
• Confirm /e/OS boots and is the same version that was flashed through web installer
• Confirm /e/OS recovery boots and is the same version that was flashed through web installer

Issues

https://gitlab.e.foundation/e/devices/backlog/-/issues/1546

10 commandments of code review

👪 ❤️ https://gitlab.e.foundation/groups/e/-/wikis/contribute/development-processes/code-review-guidelines