Appliquer l'égalité MA ⃗.MB ⃗ = 0 - Première

Whole-channel inclusion: Yvan Monka is an honest teaching channel (title sample + 3 transcripts read: All three samples lack transcripts, but titles/descriptions match the channel's consistent pattern of structured math/programming tutorials, consistent with the 'whole' verdict.); this title passed a strict title check (sonnet) after a labelling pass.