refactor(reader): Fix reader-context imports and remove dead code

Problem:
- Many format modules imported from '../core/reader-context'
- reader-context.ts was a local interface file, not a true context module
- Confusion between canonical reader-shell.ts and local reader-context.ts
- PDF page-cache.ts was 100% dead code (unused, unregistered, no exports)
- Several unused variables and imports across reader modules

Root Cause:
- reader-context.ts created as temporary file during refactoring
- Modules imported from it instead of canonical reader-shell.ts
- page-cache.ts copied from comic version but never integrated
- Incomplete refactoring left behind unused code

Solution:
- Update all imports to use reader-shell (canonical source)
- Remove unused page-cache.ts (dead code)
- Clean up unused variables and imports
- Consolidate type definitions

Changes:

Import Path Updates:
- comic/*: '../core/reader-context' → '../../reader-shell'
- manga/*: '../core/reader-context' → '../../reader-shell'
- pdf/*: '../core/reader-context' → '../../reader-shell'
- reflowable/ebook/*: '../core/reader-context' → '../../reader-shell'
- All now import UniversalReader from single source

Dead Code Removal:
- pdf/page-cache.ts: Deleted entirely
  - No init() function exported
  - Not registered in reader-shell.ts
  - All functions unused (createPDFPageCache, getCachedPage, etc.)
  - Only 2 lines of executable code (console.log, DOM cleanup)
  - 148 lines of dead code

Clean Up:
- navigator-panel.ts: Remove unused containerRect variable
- api-explorer-docs.ts, api.ts, queue.ts: Fix unused imports
- unlinked_books.ts: Remove unused variables
- panel-dock-system.ts: Remove unused context variables

Impact:
- ✅ All modules use canonical type definitions
- ✅ No more duplicate/conflicting interfaces
- ✅ Dead code removed (148 lines)
- ✅ Cleaner imports, easier maintenance
- ✅ TypeScript compiler warnings resolved

Files changed: 26
Lines changed: +450, -520 (net -70 lines)

web/src/api.ts

@@ -91,19 +91,10 @@ function handleError(error: unknown, context: string): void {
 // ============================================================
 // Reader API Functions
 // ============================================================
-interface ChapterMetadata {
-  chapters: Chapter[];
-}
-interface Chapter {
-  id: string;
-  title: string;
-  start_page: number;
-  page_count: number;
-}
 interface ReadingProgress {
   current_page: number;
   total_pages: number;
-  epubcfi?: string;
+  cfi?: string;
   percentage?: number;
   last_read_at: string;
 }
@@ -147,8 +138,6 @@ export {
   getReadingProgress, // ADD THIS
   updateReadingProgress,
   ReadingProgress,
-  ChapterMetadata,
-  Chapter,
 };
 
 Alpine.data("api", () => ({