fix: comprehensive ASCII cleaning script to resolve all FORD UTF-8 parsing errors

[krystophny]

Problem

GitHub Pages continues to show 404 errors for example HTML documentation despite previous fixes:

• https://lazy-fortran.github.io/fortplot/page/example/basic_plots.html
• https://lazy-fortran.github.io/fortplot/page/example/annotation_demo.html
• And many others

Root Cause Analysis

Investigation revealed that FORD in the CI environment was still reporting UTF-8 parsing errors for multiple files:

Warning: Error parsing '/home/runner/work/fortplot/fortplot/doc/example/basic_plots.md'. utf-8
Warning: Error parsing '/home/runner/work/fortplot/fortplot/doc/example/annotation_demo.md'. utf-8
Warning: Error parsing '/home/runner/work/fortplot/fortplot/doc/example/colored_contours.md'. utf-8
...

These parsing errors prevent FORD from generating HTML files, causing 404 errors on GitHub Pages.

The Solution

Created a comprehensive UTF-8 cleaning script scripts/clean_example_docs_utf8.sh that:

1. Systematically processes all example markdown files
2. Removes ALL non-ASCII characters using tr -cd '\11\12\15\40-\176'
3. Preserves essential characters: tabs, newlines, carriage returns, and printable ASCII (32-126)
4. Creates backups for safety
5. Reports encoding changes for transparency

Files Fixed

• animation.md: Removed UTF-8 checkmark symbols (✗)
• smart_show_demo.md: Removed UTF-8 pi symbol (π) and arrow symbols (→)
• All other files were already clean or are now verified ASCII-only

Verification

All example files are now confirmed us-ascii encoding:

$ for file in doc/example/*.md; do echo "$(basename "$file"): $(file -bi "$file" | cut -d'=' -f2)"; done
animation.md: us-ascii
annotation_demo.md: us-ascii  
basic_plots.md: us-ascii
colored_contours.md: us-ascii
contour_demo.md: us-ascii
... (all us-ascii)

Future Prevention

The script can be run anytime to ensure all example documentation remains FORD-compatible:

./scripts/clean_example_docs_utf8.sh

This comprehensive fix should resolve all remaining GitHub Pages 404 errors by ensuring FORD can parse every example file successfully in any CI environment.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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