fix(ebook-reader): Replace ReflowableBook with UniversalReader type system

BREAKING CHANGE: Unify ebook reader type system to match actual data structures

Problem:
- ReflowableBook type had direct properties (spine, resources, toc, metadata)
- UniversalReader wraps EbookCIF in cif property with runtime state
- Type mismatch caused unsafe 'as any' casts and runtime errors
- Two conflicting UniversalReader definitions existed (reader-shell vs reader-context)

Root Cause:
- Parsers return EbookCIF (nested structure)
- ReflowableBook expected flat structure
- Code mixed both approaches causing confusion

Changes:

Type System Updates:
- Replace all ReflowableBook references with UniversalReader
- Remove duplicate UniversalReader definition in reader-context.ts
- Import UniversalReader from canonical source (reader-shell.ts)
- Update all function signatures across reflowable module

Property Access Patterns:
- book.cif.spine instead of book.spine
- book.cif.resources instead of book.resources
- book.cif.toc instead of book.toc
- book.cif.metadata instead of book.metadata

Fixed Modules:
- reader-shell.ts: UniversalReader object construction
- reader-context.ts: Remove duplicate interface, import from reader-shell
- reader-navigation.ts: Remove unsafe type casts, fix property access
- reader-services.ts: Align with UniversalReader structure
- reflowable/navigation.ts: Update all navigation function signatures
- reflowable/progress-tracker.ts: Update tracker function signatures
- reflowable/parser.ts: Return UniversalReader with proper structure
- reflowable/page-calculator.ts: Update calculation function signatures
- reflowable/ebook/search.ts: Fix property access patterns
- types/reader.d.ts: Remove duplicate type definitions

Impact:
- ✅ Type-safe throughout ebook reader
- ✅ Matches actual data structures from parsers
- ✅ No more unsafe type casts
- ✅ Single source of truth for UniversalReader
- ✅ Aligns with EbookCIF format from API/parsers

Files changed: 10
Lines changed: +320, -180

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

@@ -1,17 +1,10 @@
-import { PageCalculationResult } from "../formats/reflowable/page-calculator";
-
-interface UniversalReader {
-  type: "ebook";
-  cif: any;
-  currentSpineIndex: number;
-  currentPage?: number;
-  pageCalculationResult?: PageCalculationResult;
-  currentScrollPosition?: number;
-}
+import { readerEvents, ReaderEventType } from "./reader-events";
+import { UniversalReader } from "../reader-shell";
+import { PDFDocumentProxy } from "pdfjs-dist";
 
 interface PDFReader {
   type: "pdf";
-  doc: any;
+  doc: PDFDocumentProxy;
   currentPage: number;
 }
 
@@ -87,5 +80,3 @@ export function createReaderContext(
     },
   };
 }
-
-import { readerEvents, ReaderEventType } from "./reader-events";