Add MANDATORY RULE: no silent feature removal without user consent

- Added to AI_MANDATES.md section 3 (Operational Guardrails)
- Added to CLAUDE.md as critical directive
- Ensures all feature changes are transparent and require explicit user consent
- This prevents accidental removal of functionality

CLAUDE.md

@@ -25,5 +25,13 @@ Be concise! Focus on signal over noise.
 All color changes MUST be made in `frontend/colors.mjs` ONLY.
 Run `npm run build` to sync CSS variables and Tailwind config.
 
+## ⚠️ CRITICAL: No Silent Feature Removal
+**NEVER remove, disable, or hide any existing function or functionality without:**
+1. **Explicitly informing the user** exactly what is being removed and why
+2. **Obtaining express written consent** before proceeding
+3. **If already removed**, restore immediately and apologize
+
+This applies to ALL changes: UI buttons, login modes, API endpoints, features, functionality.
+
 ---
 **Status**: ACTIVE