fix(ui): remove PN brand mark from mobile topbar; balance title with spacer

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/components/layout/mobile/mobile-topbar.tsx

@@ -9,9 +9,9 @@ import { useMobileChrome } from './mobile-layout-provider';
 
 /**
  * Fixed mobile topbar (56px + safe-area top inset). Marina-editorial premium:
- * deep-navy gradient surface with white type, the brand "PN" mark on the
- * left when there's no back affordance, and a soft glow shadow underneath
- * for depth instead of a hard divider line.
+ * deep-navy gradient surface with white type, a back arrow on the left when
+ * there's a back affordance (otherwise a balancing spacer), and a soft glow
+ * shadow underneath for depth instead of a hard divider line.
  *
  * Slots: title (auto-truncating), back arrow, primary action - all driven by
  * `useMobileChrome()` from the active page. When no page has set a title the
@@ -47,17 +47,6 @@ export function MobileTopbar() {
     portTitle ||
     'CRM';
 
-  // Brand-mark initials derived from the port slug
-  // ("port-nimara" → "PN", "marina-alpha" → "MA"). Cheap, self-contained,
-  // no extra DB round-trip.
-  const initials = portSlug
-    ? portSlug
-        .split('-')
-        .map((part) => part[0]?.toUpperCase() ?? '')
-        .join('')
-        .slice(0, 2)
-    : 'CR';
-
   return (
     <header
       className={cn(
@@ -71,15 +60,10 @@ export function MobileTopbar() {
       {backTarget ? (
         <BackButton variant="mobile" />
       ) : (
-        <div
-          aria-label={portTitle || 'Home'}
-          className={cn(
-            'size-9 shrink-0 rounded-lg flex items-center justify-center',
-            'bg-[#3a7bc8] shadow-[inset_0_1px_0_rgba(255,255,255,0.18),0_1px_2px_rgba(0,0,0,0.25)]',
-          )}
-        >
-          <span className="text-white font-bold text-[13px] tracking-tight">{initials}</span>
-        </div>
+        // No back affordance on top-level pages. Render an empty spacer the
+        // same width as the right-hand action slot so the centered title
+        // stays optically centered (the brand "PN" mark was removed here).
+        <div className="size-11 shrink-0" aria-hidden />
       )}
 
       <h1