fix(ui): annotate slider step literals as f32 for current Clippy

[thewrz]

Why

GitHub Actions now rejects three existing Iced slider .step(0.01) calls under
-D warnings with float-literal-f32-fallback. The local pinned compiler accepted
these calls, but the current CI compiler reports that this fallback is being phased
out and will become a hard error.

This failure is already present on main and blocks otherwise unrelated PRs #202
and #203. It should be fixed once on its own branch rather than duplicated in those
feature PRs.

Scope

Annotate the three slider step literals as 0.01_f32:

• src/ui/effects_panel_view.rs
• src/ui/sound_editor.rs
• src/ui/volume.rs

No behavior change and no lint suppression.

Acceptance

• Current GitHub lint job passes with -D warnings.
• Local formatting, tests, and all-target/all-feature Clippy pass.
• Exactly the three affected literals change.

Blocks CI completion for #202 and #203.