mod: Phase 3 — Re-port unmerged upstream PRs

Re-applied upstream PRs not yet merged to upstream/master:

- #1055: Byte-level framebuffer writes (fillPhysicalHSpan*,
  optimized fillRect/drawLine/fillRectDither/fillPolygon)
- #1027: Word-width cache (FNV-1a, 128-entry) and hyphenation
  early exit in ParsedText for 7-9% layout speedup
- #1068: Already present in upstream — URL hyphenation fix
- #1019: Already present in upstream — file extensions in browser
- #1090/#1185/#1217: KOReader sync improvements — binary credential
  store, document hash caching, ChapterXPathIndexer integration
- #1209: OPDS multi-server — OpdsBookBrowserActivity accepts
  OpdsServer, directory picker for downloads, download-complete
  prompt with open/back options
- #857: Dictionary activities already ported in Phase 1/2
- #1003: Placeholder cover already integrated in Phase 2

Also fixed: STR_OFF i18n string, include paths, replaced
Epub::isValidThumbnailBmp with Storage.exists, replaced
StringUtils::checkFileExtension with FsHelpers equivalents.

Made-with: Cursor

src/activities/browser/OpdsBookBrowserActivity.h

@@ -6,6 +6,7 @@
 #include <vector>
 
 #include "../Activity.h"
+#include "OpdsServerStore.h"
 #include "util/ButtonNavigator.h"
 
 /**
@@ -16,16 +17,19 @@
 class OpdsBookBrowserActivity final : public Activity {
  public:
   enum class BrowserState {
-    CHECK_WIFI,      // Checking WiFi connection
-    WIFI_SELECTION,  // WiFi selection subactivity is active
-    LOADING,         // Fetching OPDS feed
-    BROWSING,        // Displaying entries (navigation or books)
-    DOWNLOADING,     // Downloading selected EPUB
-    ERROR            // Error state with message
+    CHECK_WIFI,        // Checking WiFi connection
+    WIFI_SELECTION,    // WiFi selection subactivity is active
+    LOADING,           // Fetching OPDS feed
+    BROWSING,          // Displaying entries (navigation or books)
+    PICKING_DIRECTORY, // Directory picker subactivity is active
+    DOWNLOADING,       // Downloading selected EPUB
+    DOWNLOAD_COMPLETE, // Prompt: open book or go back to listing
+    ERROR              // Error state with message
   };
 
-  explicit OpdsBookBrowserActivity(GfxRenderer& renderer, MappedInputManager& mappedInput)
-      : Activity("OpdsBookBrowser", renderer, mappedInput) {}
+  explicit OpdsBookBrowserActivity(GfxRenderer& renderer, MappedInputManager& mappedInput,
+                                  const OpdsServer* server = nullptr)
+      : Activity("OpdsBookBrowser", renderer, mappedInput), server(server ? *server : OpdsServer{}) {}
 
   void onEnter() override;
   void onExit() override;
@@ -43,6 +47,11 @@ class OpdsBookBrowserActivity final : public Activity {
   std::string statusMessage;
   size_t downloadProgress = 0;
   size_t downloadTotal = 0;
+  std::string downloadedFilePath;
+  int promptSelection = 0;  // 0 = back to listing, 1 = open book
+
+  OpdsServer server;  // Copied at construction — safe even if the store changes during browsing
+  OpdsEntry pendingBook;
 
   void checkAndConnectWifi();
   void launchWifiSelection();
@@ -50,6 +59,9 @@ class OpdsBookBrowserActivity final : public Activity {
   void fetchFeed(const std::string& path);
   void navigateToEntry(const OpdsEntry& entry);
   void navigateBack();
-  void downloadBook(const OpdsEntry& book);
+  void launchDirectoryPicker(const OpdsEntry& book);
+  void onDirectoryPickerResult(const ActivityResult& result);
+  void downloadBook(const OpdsEntry& book, const std::string& directory);
+  void executePromptAction(int action);
   bool preventAutoSleep() override { return true; }
 };