fix(header): tab title fade is resting-state only; clearer separators

The title fade no longer sits on controls: it lifts while the tab is
hovered or its controls/menu are open (hard clip instead) and is not
applied at all while the active tab renames. The active tab clips its
title instead of showing an ellipsis, matching inactive tabs. Tab
separators drop the extra transparency that made them nearly
invisible.

packages/ui/src/components/layout/Header.tsx

@@ -1855,7 +1855,7 @@ export const Header: React.FC = () => {
                   </button>
                 </form>
               ) : (
-                <span className="truncate text-[13px] font-medium leading-4 text-foreground max-w-full">
+                <span className="block overflow-hidden whitespace-nowrap text-[13px] font-medium leading-4 text-foreground max-w-full">
                   {isNewSessionDraftOpen ? t('sessions.switcher.draftTitle') : currentSessionTitle}
                 </span>
               )}

packages/ui/src/components/layout/SessionTabsStrip.tsx

@@ -219,8 +219,9 @@ const SessionTabItem: React.FC<{
                       onClose(tab.id);
                     }
                   }}
+                  data-controls-open={overlayVisible ? 'true' : 'false'}
                   className={cn(
-                    'group/session-tab relative flex h-7 w-full min-w-0 select-none items-center rounded-md px-2',
+                    'session-tab group/session-tab relative flex h-7 w-full min-w-0 select-none items-center rounded-md px-2',
                     isActive
                       ? 'bg-interactive-selection'
                       : cn(
@@ -235,7 +236,11 @@ const SessionTabItem: React.FC<{
                     overlayVisible && 'pr-10',
                   )}
                   >
-                    <div className="session-tab-title min-w-0 flex-1 overflow-hidden whitespace-nowrap">
+                    <div className={cn(
+                      'min-w-0 flex-1 overflow-hidden whitespace-nowrap',
+                      !suppressControls && 'session-tab-title',
+                    )}
+                    >
                       {isActive ? children : (
                         <span className="text-[13px] font-medium leading-4">{title}</span>
                       )}