Remove TUI codepath and boot straight to GUI

[KEYTRON]

Summary

• drop the TUI initialization/demo flow from kernel_main so the kernel only brings up the graphics stack and GUI desktop
• simplify graphics bring-up logging and stop creating sample GUI widgets ahead of the desktop runtime
• rename the GRUB entry to "MyOS GUI" to reflect the GUI-only boot option

Testing

• make -C kernel

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Codex Task

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Run build_iso.sh from repo root

The new workflow invokes QEMU_EXIT=1 ./utils/build_iso.sh (lines 21‑24) while staying in the repository root, but utils/build_iso.sh immediately does cd ../kernel (line 6 of that script) and therefore assumes it was launched from the utils/ directory. Running it from the root leaves the working directory unchanged, so the cd fails with cd: ../kernel: No such file or directory, after which the subsequent make commands run in the wrong directory and the script exits with an error (reproduced locally with the same command). As a result, the CI job will always fail before producing an ISO. Change the workflow to cd utils (or call the script via bash utils/build_iso.sh after pushd utils) before invoking the script.

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