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/queue.ts

@@ -155,7 +155,7 @@ function renderQueueItems(items: QueueItemResponse[]): void {
     .join("");
 }
 
-function showQueueItemModal(itemId: string): void {
+function showQueueItemModal(): void {
   const modal = document.getElementById("queue-item-modal");
   const detailsContainer = document.getElementById("queue-item-details");