reader: convert feature modules to Feature Registration Pattern

- Add init(context) exported function to each feature module
- Store module-level context reference for event handlers
- Fix gestures.ts to use library_type_name instead of library_type
- Features: gestures, keyboard-shortcuts, navigator-panel, offline-manager,
  panel-dock-system, progress-indicator, reading-speed-tracker

web/src/reader/features/progress-indicator.ts

@@ -3,7 +3,11 @@ interface ProgressDisplay {
   mode: "pages" | "chapter" | "percentage" | "time-left";
   text: string;
 }
-export async function init(context: ReaderContext): Promise<void> {
+
+let context: ReaderContext;
+
+export async function init(readerContext: ReaderContext): Promise<void> {
+  context = readerContext;
   context.events.on("pageChanged", () => {
     updateProgressDisplay(context);
   });