Improve ESP auto-mount detection across Fedora layouts

[GlitchSlayed]

Motivation

• Automatic ESP detection/mounting was failing on some Fedora systems where the ESP is not mounted at /boot/efi or /efi, leading to a hard failure during setup.
• The goal is to make ESP discovery more robust by checking additional common mount points and scanning mounted FAT/VFAT filesystems for an EFI directory.

Description

• Add ESP_MOUNT_CANDIDATES containing /boot/efi, /efi, /boot, /boot/EFI, and /esp and iterate these when attempting fstab-based mounts.
• Implement find_mounted_esp_target() which first checks the candidate mount points and then falls back to scanning findmnt for FAT/VFAT mounts that contain an EFI directory.
• Replace direct /boot/efi//efi lookups in ensure_esp_mounted() and the generated uki-build.sh template with the new detection and candidate-iteration logic, and attempt mounting the detected ESP device across all candidates.
• Improve error messages to list the checked locations and update README.md to document the expanded ESP handling.

Testing

• Ran bash -n uki-setup.sh to verify there are no syntax errors; the check succeeded.
• Ran the repository test script bash tests/test_uki_setup.sh, which verifies generation of the uki-build.sh helper and kernel-install plugin and it completed successfully.
• End-to-end local checks in the test harness completed without failures.

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Codex Task

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[chatgpt-codex-connector]

Validate candidate mount type before accepting it as ESP

The new find_mounted_esp_target() returns the first mounted candidate path without checking that it is actually an EFI System Partition. On systems with a separate ext4 /boot and an unmounted ESP (e.g. /boot/efi not mounted), this now returns /boot as the ESP, so ensure_esp_mounted exits early and later efibootmgr registration targets the /boot partition instead of the FAT ESP. That can produce unusable boot entries and place UKIs on a partition firmware cannot read.

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