fix(auth): login logo was blank, AppIcon app-icon set isn't Image()-loadable

Image("AppIcon") resolved to nothing at runtime (confirmed live) — App
Icon-type asset catalog entries aren't reliably retrievable through
Image(_:)/UIImage(named:) the way a normal Image Set is. Added AppLogo,
a plain Image Set duplicating the same outpost-ios-1024.png artwork, and
pointed AuthHeaderView at that instead.

Outpost/Assets.xcassets/AppLogo.imageset/Contents.json

@@ -0,0 +1,21 @@
+{
+  "images" : [
+    {
+      "filename" : "outpost-ios-1024.png",
+      "idiom" : "universal",
+      "scale" : "1x"
+    },
+    {
+      "idiom" : "universal",
+      "scale" : "2x"
+    },
+    {
+      "idiom" : "universal",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

Outpost/Features/Auth/AuthHeaderView.swift

@@ -3,10 +3,12 @@ import SwiftUI
 struct AuthHeaderView: View {
     var body: some View {
         VStack(spacing: 12) {
-            // Renders whichever platform variant AppIcon.appiconset has for
-            // the current destination — same asset Xcode uses for the
-            // Dock/Home Screen icon, so this can't drift from it separately.
-            Image("AppIcon")
+            // A plain Image Set, not the AppIcon *app icon* asset — App Icon
+            // sets aren't reliably resolvable through Image(_:)/UIImage
+            // (named:) at runtime (confirmed live: showed nothing). This is
+            // the same source artwork (outpost-ios-1024.png) duplicated
+            // into a normal image set so SwiftUI can actually load it.
+            Image("AppLogo")
                 .resizable()
                 .scaledToFit()
                 .frame(width: 72, height: 72)