fix: resolve TypeScript errors in reader module

- reader-context.ts: fix event type to use ReaderEventType instead of string
- page-calculator.ts: add pagesInChapter property to ChapterPageInfo interface
- reader-navigation.ts: remove unused getScrollPositionForPage import

web/src/reader/core/reader-context.ts

@@ -1,8 +1,5 @@
-import type { ReaderMetadata } from "../../types/reader";
 import { PageCalculationResult } from "../ebook/page-calculator";
 
-type ReaderType = "ebook" | "pdf" | "comic" | "manga";
-
 interface UniversalReader {
   type: "ebook";
   cif: any;
@@ -79,10 +76,12 @@ export function createReaderContext(
       progressDisplay: document.getElementById("progress-display"),
     },
     events: {
-      on: (event: string, handler: Function) => readerEvents.on(event, handler),
-      emit: (event: string, data?: any) => readerEvents.emit(event, data),
+      on: (event: ReaderEventType, handler: Function) =>
+        readerEvents.on(event, handler),
+      emit: (event: ReaderEventType, data?: any) =>
+        readerEvents.emit(event, data),
     },
   };
 }
 
-import { readerEvents } from "./reader-events";
+import { readerEvents, ReaderEventType } from "./reader-events";