Refactor kernel enumeration and add UKI reconciliation/retention

[GlitchSlayed]

Motivation

• Ensure UKIs are created and managed for the full set of kernels actually installed via RPM rather than only for the running kernel.
• Prevent accidental removal of UKIs for kernels until a successful boot is confirmed to avoid removing a working boot target during upgrades.
• Provide a maintenance mode to reconcile installed kernels, rebuild missing UKIs, and prune stale artifacts in a controlled, auditable way.

Description

• Add list_installed_kernels() helper (in uki-setup.sh and the generated uki-build.sh) that enumerates rpm -q kernel results, normalizes them (strip kernel-) and yields versions that have /lib/modules/<ver>/vmlinuz.
• Change initial setup build phase to iterate list_installed_kernels() and build UKIs for every installed kernel instead of only uname -r.
• Implement a --reconcile maintenance mode in the generated uki-build.sh that rebuilds UKIs for all installed kernels, detects stale UKIs on the ESP, and prunes stale UKIs/EFI entries only after a boot-success marker exists under BOOT_SUCCESS_DIR (default /var/lib/uki-ukify/boot-success).
• Update the kernel-install plugin so add, remove, and other invocations call the reconcile mode (instead of deleting by the event kernel version), add helper delete_uki_and_entry() to remove both the UKI file and corresponding EFI boot entry, and document the retention/confirmation behavior in the post-install summary with a manual reconcile invocation (--reconcile) and example confirmation command.

Testing

• Ran bash -n uki-setup.sh to verify the modified script syntax and it passed.
• Executed the repository tests with bash tests/test_uki_setup.sh and the test script passed.
• Ran bash -n tests/test_uki_setup.sh to lint the test and it passed.

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Codex Task