feat: Search tab with character picker and unified tab bar navigation

Adds Search tab to MyLibraryActivity with character picker for building
search queries, result navigation with long press jump-to-end support,
and Bookmarks tab integration. Implements consistent tab bar navigation
across all tabs - pressing Up from top of any list enters tab bar mode
with visible cursor indicators, Left/Right switches tabs, Down enters
list at top, and Up jumps to bottom of list.

src/activities/home/MyLibraryActivity.h

@@ -19,9 +19,25 @@ struct ThumbExistsCache {
   bool exists = false;       // Whether thumbnail exists
 };
 
+// Search result for the Search tab
+struct SearchResult {
+  std::string path;
+  std::string title;
+  std::string author;
+  int matchScore = 0;  // Higher = better match
+};
+
+// Book with bookmarks info for the Bookmarks tab
+struct BookmarkedBook {
+  std::string path;
+  std::string title;
+  std::string author;
+  int bookmarkCount = 0;
+};
+
 class MyLibraryActivity final : public Activity {
  public:
-  enum class Tab { Recent, Lists, Files };
+  enum class Tab { Recent, Lists, Bookmarks, Search, Files };
   enum class UIState { Normal, ActionMenu, Confirming, ListActionMenu, ListConfirmingDelete, ClearAllRecentsConfirming };
   enum class ActionType { Archive, Delete, RemoveFromRecents, ClearAllRecents };
 
@@ -32,6 +48,7 @@ class MyLibraryActivity final : public Activity {
   Tab currentTab = Tab::Recent;
   int selectorIndex = 0;
   bool updateRequired = false;
+  bool inTabBar = false;  // true = focus on tab bar for switching tabs (all tabs)
 
   // Action menu state
   UIState uiState = UIState::Normal;
@@ -61,6 +78,17 @@ class MyLibraryActivity final : public Activity {
   int listMenuSelection = 0;  // 0 = Pin/Unpin, 1 = Delete
   std::string listActionTargetName;
 
+  // Bookmarks tab state
+  std::vector<BookmarkedBook> bookmarkedBooks;
+
+  // Search tab state
+  std::string searchQuery;
+  std::vector<SearchResult> searchResults;
+  std::vector<SearchResult> allBooks;  // Cached index of all books
+  std::vector<char> searchCharacters;  // Dynamic character set from library
+  int searchCharIndex = 0;             // Current position in character picker
+  bool searchInResults = false;        // true = navigating results, false = in character picker
+
   // Files tab state (from FileSelectionActivity)
   std::string basepath = "/";
   std::vector<std::string> files;
@@ -69,6 +97,7 @@ class MyLibraryActivity final : public Activity {
   const std::function<void()> onGoHome;
   const std::function<void(const std::string& path, Tab fromTab)> onSelectBook;
   const std::function<void(const std::string& listName)> onSelectList;
+  const std::function<void(const std::string& path, const std::string& title)> onSelectBookmarkedBook;
 
   // Number of items that fit on a page
   int getPageItems() const;
@@ -79,6 +108,9 @@ class MyLibraryActivity final : public Activity {
   // Data loading
   void loadRecentBooks();
   void loadLists();
+  void loadBookmarkedBooks();
+  void loadAllBooks();
+  void updateSearchResults();
   void loadFiles();
   size_t findEntry(const std::string& name) const;
 
@@ -88,10 +120,16 @@ class MyLibraryActivity final : public Activity {
   void render() const;
   void renderRecentTab() const;
   void renderListsTab() const;
+  void renderBookmarksTab() const;
+  void renderSearchTab() const;
   void renderFilesTab() const;
   void renderActionMenu() const;
   void renderConfirmation() const;
 
+  // Search character picker helpers
+  void buildSearchCharacters();
+  void renderCharacterPicker(int y) const;
+
   // Action handling
   void openActionMenu();
   void executeAction();
@@ -114,13 +152,15 @@ class MyLibraryActivity final : public Activity {
                              const std::function<void()>& onGoHome,
                              const std::function<void(const std::string& path, Tab fromTab)>& onSelectBook,
                              const std::function<void(const std::string& listName)>& onSelectList,
+                             const std::function<void(const std::string& path, const std::string& title)>& onSelectBookmarkedBook = nullptr,
                              Tab initialTab = Tab::Recent, std::string initialPath = "/")
       : Activity("MyLibrary", renderer, mappedInput),
         currentTab(initialTab),
         basepath(initialPath.empty() ? "/" : std::move(initialPath)),
         onGoHome(onGoHome),
         onSelectBook(onSelectBook),
-        onSelectList(onSelectList) {}
+        onSelectList(onSelectList),
+        onSelectBookmarkedBook(onSelectBookmarkedBook) {}
   void onEnter() override;
   void onExit() override;
   void loop() override;