Embed the English version in the main README

[Mamat79]

What changed

• adds a prominent English link directly below the README badges
• embeds the complete English presentation below the French version on the same GitHub page
• keeps the standalone README_EN.md link for direct sharing
• adds stable French and English anchors for quick navigation in both directions

Why

English-speaking visitors can now reach and read the complete English presentation without leaving the main repository page.

Validation

• embedded English content matches README_EN.md exactly, except for the back-to-French anchor
• top English link and French return anchor are present
• git diff --check passes
• documentation-only change; application and release binaries are unchanged