Add IL comparison path copy buttons to HTML reports

[Widthdom]

Summary

• add a distinct two-file copy button beside each ILMatch / ILMismatch label when ShouldOutputILText=true
• embed the absolute old/new IL output roots in diff_report.html and copy a platform-appropriate quoted path pair for WinMerge, diff, and other text-based diff tools
• use the report's shared translucent fading tooltip, show a brief check mark on success, and show a red exclamation mark plus a browser alert on failure; no copy toast is emitted
• hide tooltips after a pointer click followed by mouse leave by limiting focus-driven display to :focus-visible, while preserving keyboard-focus behavior
• synchronize the POSIX-style live HTML sample, English/Japanese user guide, changelog, and regression tests

Root cause

The shared tooltip rule used .btn-tooltip-wrap:focus-within, so clicking a copy button left focus inside the wrapper and kept the tooltip visible even after hover ended. The rule now targets the actual buttons with :focus-visible, which keeps keyboard accessibility without pinning the tooltip after pointer clicks.

Testing

• npm run test:js -- --runInBand — 175 passed at the current head
• dotnet test FolderDiffIL4DotNet.Tests/FolderDiffIL4DotNet.Tests.csproj -c Release --no-restore --disable-build-servers -m:1 --filter FullyQualifiedName~HtmlReport --nologo — 240 passed at the current head
• env GIT_CONFIG_COUNT=1 GIT_CONFIG_KEY_0=commit.gpgsign GIT_CONFIG_VALUE_0=false dotnet test FolderDiffIL4DotNet.Tests/FolderDiffIL4DotNet.Tests.csproj -c Release --no-restore --disable-build-servers -m:1 --nologo — 2016 passed, 1 skipped at the current head
• sample HTML script/DOM validation — JavaScript syntax valid; 11 IL rows mapped to 11 IL path buttons; no duplicate markup IDs; POSIX IL prefixes; no toast or JS tooltip-state class
• git diff --check — clean

Notes

• The full Release suite needs commit signing disabled for its temporary Git-repository fixtures in this local environment; with that test-only override, it passes.
• The in-app browser blocks local file:// navigation, so visual verification was limited to the supplied screenshots plus script/DOM/CSS validation.
• The project-wide dotnet format --verify-no-changes command still reports existing whitespace differences in unrelated source regions; this change does not rewrite those files.
• cdidx v1.39.3 was rerun after the latest follow-up commit. It indexed the changed C#/JS/CSS/Markdown/HTML files, but the overall run remains partial because of the known JSON worker failure tracked in v1.39.3: JSON symbol-extraction worker fails with JsonSerializerIsReflectionDisabled, leaving rebuilt index partial CodeIndex#4709.