macOS: Fix new window focus when created from quick terminal (#5834)

## Root Cause

The issue has two aspects:

1. The window creation process didn't explicitly force focus on the new
window after showing it.
2. More fundamentally, we were relying on `NSApp.isActive` to determine
whether to activate the application, which is problematic because:
- When creating a window from quick terminal, the application is already
"active" but this active state is owned by the quick terminal
- The [`NSApp.isActive`
check](4cfe5522db/macos/Sources/Features/Terminal/TerminalManager.swift (L100))
doesn't accurately reflect our intent - creating a new window is an
explicit user action that should always result in that window gaining
focus

## Solution

Removing the `NSApp.isActive` check.

```swift
// Before
if !NSApp.isActive {
    NSApp.activate(ignoringOtherApps: true)
}

// After
NSApp.activate(ignoringOtherApps: true)
```

Fixes #5688

macos/Sources/Features/Terminal/TerminalManager.swift

@@ -95,11 +95,8 @@ class TerminalManager {
             }
         }
 
-        // If our app isn't active, we make it active. All new_window actions
-        // force our app to be active.
-        if !NSApp.isActive {
+        // All new_window actions force our app to be active.
         NSApp.activate(ignoringOtherApps: true)
-        }
 
         // We're dispatching this async because otherwise the lastCascadePoint doesn't
         // take effect. Our best theory is there is some next-event-loop-tick logic