Tweak settings footer button style/visibility

[poliver]

Tweaks footer buttons to improve scrollable visibility. Before, they were always visible taking up vertical space, even when disabled.

• Hides settings footer buttons when config has not changed
• Footer buttons are superimposed on scrollable content when visible. Buttons are elevated and tinted for primary/secondary action. Container is transparent.

Before	After
Screen_recording_20251013_165531.mp4	Screen_recording_20251013_165342.mp4

[codecov]

Codecov Report

❌ Patch coverage is 0% with 27 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.39%. Comparing base (43400f8) to head (9428118).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
.../settings/radio/component/RadioConfigScreenList.kt	0.00%	27 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main   #3458      +/-   ##
========================================
- Coverage   0.39%   0.39%   -0.01%     
========================================
  Files        301     301              
  Lines      17849   17864      +15     
  Branches    2140    2141       +1     
========================================
  Hits          71      71              
- Misses     17762   17777      +15     
  Partials      16      16              

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