fix: reassign utility part slots

[scarf005]

Purpose of change (The Why)

Closes #8489.
Vehicle utility parts were still sharing the legacy anywhere slot, which blocked combinations like foldable seats with NBC seals on the same tile.

Describe the solution (The How)

Reassign former anywhere parts to more specific layers (center, on_ceiling, on_roof) and give on_ceiling explicit ordering.
Add regression tests for the slot remap and for installing utility parts on a folding-seat tile.

Testing

• cmake --build --preset linux-full --target astyle
• cmake --build --preset linux-full --target style-json-parallel
• cmake --build --preset linux-full --target cata_test-tiles
• ./out/build/linux-full/tests/cata_test-tiles "vehicle_part_utility_slots_are_not_anywhere"
• ./out/build/linux-full/tests/cata_test-tiles "folding_seat_tile_accepts_other_utility_parts"
• ./build-scripts/lint-json.sh

Additional context

No existing docs appear to cover vehicle part slot layering.

Checklist

Mandatory

• I wrote the PR title in conventional commit format.
• I ran the code formatter.
• I linked any relevant issues using github keyword syntax like closes #1234 in Summary of the PR so it can be closed automatically.
• I've committed my changes to new branch that isn't main so it won't cause conflict when updating main branch later.

Optional

• This is a C++ PR that modifies JSON loading or behavior.
• I have documented the changes in the appropriate location in the docs/ folder.
• If documentation for this feature does not exist, please write it or at least note its lack in PR description.

^{PR opened by gpt-5.4 high on opencode}

[chaosvolt]

This one defeats the main purpose of foldable seats, being used like a hammock tucked into any passable tile to make it one that can be sat at, assign NPCs to, etc. Maybe on_ceiling on the basis of being hung from the ceiling I guess?