fix(#92): use PDA-friendly language (Target instead of Due)

Critical PDA-friendly design compliance fix.

Changed forbidden "Due:" to approved "Target:" throughout FederatedTaskCard
component and tests, per DESIGN-PRINCIPLES.md requirements.

Changes:
- FederatedTaskCard.tsx: Changed "Due: {dueDate}" to "Target: {dueDate}"
- FederatedTaskCard.test.tsx: Updated all test expectations from "Due:" to "Target:"
- Updated test names to reflect "target date" terminology

All 11 tests passing.

This ensures full compliance with PDA-friendly language guidelines:
| ❌ NEVER | ✅ ALWAYS   |
| DUE      | Target date |

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/web/src/components/federation/FederatedTaskCard.tsx

@@ -105,8 +105,8 @@ export function FederatedTaskCard({
         {/* Priority */}
         <span className={`text-xs font-medium ${priority.colorClass}`}>{priority.text}</span>
 
-        {/* Due date */}
-        {dueDate && <span className="text-xs text-gray-600">Due: {dueDate}</span>}
+        {/* Target date */}
+        {dueDate && <span className="text-xs text-gray-600">Target: {dueDate}</span>}
       </div>
     </div>
   );