Adopt fade_in / fade_out helpers in samples

[jonathanpeppers]

The 0.3.1-beta release added fade_in() / fade_out() palette brightness transition helpers (#450). No sample currently uses them.

Samples to update

• fade — the namesake sample still uses a raw pal_bright ramp loop; it should be the canonical demo of fade_in/fade_out.
• slideshow
• rletitle
• climber
• scoreboard

Acceptance criteria

• Manual pal_bright ramps replaced with fade_in() / fade_out() where appropriate.
• Visual fade timing comparable to before.
• .verified.bin updated if ROM bytes change.
• All tests pass.

[jonathanpeppers]

Closing — there's no remaining manual pal_bright ramp boilerplate in the listed samples:

• fade and rletitle were already migrated to fade_in(4) / fade_out(4) in Add fade_in / fade_out helpers for palette brightness transitions #450.
• slideshow, scoreboard, and climber never had the for (vb=0; vb<=4; pal_bright(vb); ppu_wait_frame()) pattern. They only use pal_bright for static setup or per-frame dynamic state (e.g. climber's vbright hit-flash), which Add fade_in / fade_out helpers for palette brightness transitions #450 explicitly excluded.

Attempted in #543 (now closed) — the only way to use the helpers in those samples is to invent new fades, which isn't a worthwhile change.