refactor(installer): replace SourceDirectory with Mode/Version fields in InstallContext

src/ClaudeDo.Installer/Core/InstallContext.cs

@@ -2,10 +2,15 @@ namespace ClaudeDo.Installer.Core;
 
 public sealed class InstallContext
 {
-    // WelcomePage
-    public string SourceDirectory { get; set; } = "";
+    // WelcomePage / install destination
     public string InstallDirectory { get; set; } = @"C:\Program Files\ClaudeDo";
 
+    // Mode + versions (set by App startup after InstallModeDetector runs)
+    public InstallerMode Mode { get; set; } = InstallerMode.FreshInstall;
+    public string? InstallerVersion { get; set; }   // from this installer's assembly
+    public string? InstalledVersion { get; set; }   // from install.json (or set by DownloadAndExtractStep)
+    public string? LatestVersion { get; set; }      // from Gitea API (may be null if offline)
+
     // PathsPage
     public string DbPath { get; set; } = "~/.todo-app/todo.db";
     public string LogRoot { get; set; } = "~/.todo-app/logs";
@@ -27,6 +32,4 @@ public sealed class InstallContext
 
     // InstallPage
     public bool CreateDesktopShortcut { get; set; } = true;
-
-    public string? InstalledVersion { get; set; }
 }