The Gambler's Ruin Theorem Pronounces a Death Sentence: If the Direction Is Wrong, Even a Huge Principal Will Go to Zero! Backtesting Four Major Crashes with 100% Accuracy; Applying 2026 Data to China, 290 to 430 Trillion in Wealth to Be Annihilated in the Next Decade, 60 to 80 Million Households to Slide Down the Social Ladder—Are You in the Kill Zone?