feat: port upstream OPDS improvements (PRs #1207, #1209)

Port two upstream PRs:

- PR #1207: Replace manual chunked download loop with
  HTTPClient::writeToStream via a FileWriteStream adapter, improving
  reliability for OPDS file downloads including chunked transfers.

- PR #1209: Add support for multiple OPDS servers with a new
  OpdsServerStore (JSON persistence with MAC-based password obfuscation),
  OpdsServerListActivity and OpdsSettingsActivity UIs, per-server
  credentials passed to HttpDownloader, web UI management endpoints,
  and migration from legacy single-server settings.

Made-with: Cursor

src/main.cpp

@@ -19,6 +19,7 @@
 #include "CrossPointState.h"
 #include "KOReaderCredentialStore.h"
 #include "MappedInputManager.h"
+#include "OpdsServerStore.h"
 #include "RecentBooksStore.h"
 #include "activities/boot_sleep/BootActivity.h"
 #include "activities/boot_sleep/SleepActivity.h"
@@ -28,6 +29,7 @@
 #include "activities/home/RecentBooksActivity.h"
 #include "activities/network/CrossPointWebServerActivity.h"
 #include "activities/reader/ReaderActivity.h"
+#include "activities/settings/OpdsServerListActivity.h"
 #include "activities/settings/SettingsActivity.h"
 #include "activities/util/FullScreenMessageActivity.h"
 #include "components/UITheme.h"
@@ -261,7 +263,18 @@ void onGoToMyLibraryWithPath(const std::string& path, bool initialSkipRelease) {
 
 void onGoToBrowser() {
   exitActivity();
-  enterNewActivity(new OpdsBookBrowserActivity(renderer, mappedInputManager, onGoHome));
+  const auto& servers = OPDS_STORE.getServers();
+  if (servers.size() == 1) {
+    enterNewActivity(new OpdsBookBrowserActivity(renderer, mappedInputManager, onGoHome, servers[0]));
+  } else {
+    enterNewActivity(new OpdsServerListActivity(renderer, mappedInputManager, onGoHome, [](size_t serverIndex) {
+      const auto* server = OPDS_STORE.getServer(serverIndex);
+      if (server) {
+        exitActivity();
+        enterNewActivity(new OpdsBookBrowserActivity(renderer, mappedInputManager, onGoHome, *server));
+      }
+    }));
+  }
 }
 
 void onGoHome() {
@@ -343,6 +356,7 @@ void setup() {
 
   I18N.loadSettings();
   KOREADER_STORE.loadFromFile();
+  OPDS_STORE.loadFromFile();
   BootNtpSync::start();
   UITheme::getInstance().reload();
   ButtonNavigator::setMappedInputManager(mappedInputManager);