fix: Reader stuck on loading — guard checked isLoading which was true

loadInitial() had guard !isLoading but isLoading defaults to true,
so it returned immediately without loading. Replaced with hasLoadedOnce
flag to prevent double-loading without blocking the first call.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ios/Platform/Platform/Features/Reader/ViewModels/ReaderViewModel.swift

@@ -41,8 +41,11 @@ final class ReaderViewModel {
 
     // MARK: - Load
 
+    private var hasLoadedOnce = false
+
     func loadInitial() async {
-        guard !isLoading else { return }
+        guard !hasLoadedOnce else { return }
+        hasLoadedOnce = true
         isLoading = true
         error = nil