Fix registration enumeration + contact detail panel name sync

M-01: Unify registration error messages to prevent username/email
enumeration — both now return the same generic message.

Bug fix: Contact detail panel header and initials now use shared_fields
for umbral contacts instead of stale Person record first_name/last_name.
The table list already did this via sf() helper; the detail panel header
and getPersonInitialsName were bypassing it.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/routers/auth.py

@@ -441,7 +441,7 @@ async def register(
         select(User).where(User.username == data.username)
     )
     if existing.scalar_one_or_none():
-        raise HTTPException(status_code=400, detail="Registration could not be completed. Please try a different username.")
+        raise HTTPException(status_code=400, detail="Registration could not be completed. Please check your details and try again.")
 
     # Check email uniqueness (generic error to prevent enumeration)
     if data.email:

frontend/src/components/people/PeoplePage.tsx

@@ -60,7 +60,11 @@ function StatCounter({
 // Helpers
 // ---------------------------------------------------------------------------
 function getPersonInitialsName(p: Person): string {
-  const parts = [p.first_name, p.last_name].filter(Boolean);
+  const firstName = p.is_umbral_contact && p.shared_fields?.first_name
+    ? String(p.shared_fields.first_name) : p.first_name;
+  const lastName = p.is_umbral_contact && p.shared_fields?.last_name
+    ? String(p.shared_fields.last_name) : p.last_name;
+  const parts = [firstName, lastName].filter(Boolean);
   return parts.length > 0 ? parts.join(' ') : p.name;
 }
 
@@ -428,7 +432,11 @@ export default function PeoplePage() {
         </div>
         <div className="min-w-0">
           <div className="flex items-center gap-2">
-            <h3 className="font-heading text-lg font-semibold truncate">{p.name}</h3>
+            <h3 className="font-heading text-lg font-semibold truncate">{
+              p.is_umbral_contact && p.shared_fields
+                ? [sf(p, 'first_name'), sf(p, 'last_name')].filter(Boolean).join(' ') || p.name
+                : p.name
+            }</h3>
             {p.is_umbral_contact && (
               <Ghost className="h-4 w-4 text-violet-400 shrink-0" />
             )}