Make exception display color-aware for DocumenterVitepress

[ocots]

This PR makes exception display color-aware to work correctly with DocumenterVitepress, and adds the full DocumenterVitepress migration setup.

Changes

Exception display color-aware

• Add _apply_ansi(s, code, io) helper that checks get(io, :color, false) before applying ANSI codes
• Update all ANSI helpers (_dim, _bold, _red, _yellow, _green) to accept io parameter
• Propagate io to all call sites in display functions (_print_colored, _print_pipe_field, _format_user_friendly_error)
• Add IOContext(stdout, :color => false) in @repl block to avoid raw ANSI codes in VitePress output
• Add color-aware tests to verify both branches (color=true/false)

Documentation

• Fix URI malformed error in coverage.md (heading with % literal)
• Add MIGRATION.md with complete DocumenterVitepress migration guide
• Document ANSI color handling workaround for @repl blocks (issue [General] New release #321)
• Add Vitepress configuration files (config, theme, components)
• Add remote assets configuration for control-toolbox CSS/JS

Rationale

DocumenterVitepress does not automatically convert ANSI escape codes to HTML in @repl blocks (unlike @example blocks). This causes raw ANSI codes to appear in the generated markdown. The workaround is to use IOContext(stdout, :color => false) in @repl blocks, and make custom display functions color-aware by checking get(io, :color, false).

This ensures:

• REPL / GitHub Actions → colors enabled (:color => true by default)
• Documenter / VitePress → plain text when wrapped with IOContext(stdout, :color => false)

Tests

• Suite ciblée exceptions: 355 tests ✓
• Suite complète: 1242 tests ✓
• Documentation build: successful, no raw ANSI codes in output