fix: replace SVG RECORDBUTTON with Material Icons ligature in toolbar

[ssz2605]

Description

PR #7757 replaced innerHTML with textContent for security, which broke
the Record button , RECORDBUTTON is an SVG string, not a Material Icons
ligature, so textContent cannot render it. PR #7782 reverted to innerHTML
as a temporary fix, but left the original problems unsolved:

• innerHTML still used (the exact thing fix: replace innerHTML with textContent across core widgets for security #7757 tried to eliminate)
• RECORDBUTTON SVG constant still exists in artwork.js
• recorder.js still targets rec_inside, a DOM element only created by
  the SVG. If anyone changes the SVG, recording breaks again.
• Recording state uses setAttribute("fill","red") instead of CSS

This PR fixes all of them:

• Add fiber_manual_record to #record in index.html, matching Play/Stop
• Remove dynamic icon creation from toolbar-ui.js
• Refactor recorder.js to use CSS class on #record instead of rec_inside
• Add #record.recording CSS for blink animation and red color
• Remove dead RECORDBUTTON SVG constant from artwork.js
• Remove unused RECORDBUTTON imports from toolbar-ui.js and turtledefs.js
• Update tests to reflect static icon and class-based recording state

PR Category

• Bug Fix

[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.00%. Comparing base (3aa560a) to head (0c205d8).

Files with missing lines	Patch %	Lines
js/activity/recorder.js	25.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7785      +/-   ##
==========================================
- Coverage   59.00%   59.00%   -0.01%     
==========================================
  Files         175      175              
  Lines       57916    57911       -5     
==========================================
- Hits        34172    34169       -3     
+ Misses      23744    23742       -2     

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