refactor: Convert all reader features to Feature Registration Pattern

Complete the Feature Registration Pattern refactoring across all reader
modules. Each feature now exports an init(context) function and uses the
event-based architecture for loose coupling.

## Comic Features (6 files)
- background-color.ts: Background color picker with toggle
- chapter-markers.ts: Visual chapter indicators
- page-cache.ts: 5-page ahead prefetch with cleanup
- page-order.ts: Auto-detect Japanese vs Western order
- page-scrubber.ts: Quick navigation slider
- panel-gap.ts: Adjustable panel gap controls

## Ebook Features (6 files)
- copy-handler.ts: Text copying with citation
- dictionary-popup.ts: Word lookup integration
- font-loader.ts: 8 bundled libre fonts
- search.ts: Full-text search across spine
- typography-engine.ts: Font rendering and hyphenation

## Manga Features (4 files)
- reading-direction.ts: RTL/LTR/vertical detection
- rtl-navigator.ts: Reversed page turn direction
- settings.ts: Webtoon mode and transitions
- vertical-scroll-mode.ts: Infinite scroll with lazy loading

## PDF Features (3 files)
- pdf-navigation.ts: Page turning, zoom, fit modes
- pdf-text-selection.ts: Highlight creation via backend
- annotation-layer.ts: Render highlights and notes

## Root-Level Features (3 files)
- offline-manager.ts: PWA service worker and sync
- reading-speed-tracker.ts: Pages/words per minute tracking
- settings-manager.ts: Per-user settings with localStorage fallback

## Core Infrastructure (1 file)
- parser-manager.ts: Fixed import paths for all parsers

## Key Changes
- All features use init(context) pattern
- Event-based communication via context.events.on/emit
- No direct DOM manipulation in feature exports
- State managed within feature closures
- Clean initialization and teardown
- Zero functionality lost - all features preserved

Total: 23 files converted to unified architecture

web/src/reader/comic/page-order.ts

@@ -1,7 +1,43 @@
 // Page order presets for manga/comics
 // Auto-detect Japanese vs Western reading order
-// Allow user override in case detection is wrong
-// Procedural implementation (no OOP)
+// Feature Registration Pattern implementation
+
+import type { ReaderContext } from "../core/reader-context";
+
+export function init(context: ReaderContext): void {
+  let state: PageOrderState | null = null;
+
+  context.events.on("reader:loaded", (detail: { totalPages: number; pageNames: string[] }) => {
+    state = createPageOrderState(detail.totalPages, detail.pageNames);
+  });
+
+  context.events.on("page-order:set", (detail: { mode: PageOrderMode }) => {
+    if (state) {
+      setPageOrderMode(state, detail.mode, context);
+    }
+  });
+
+  context.events.on("page-order:get", () => {
+    if (state) {
+      const order = getPageOrder(state);
+      context.events.emit("page-order:current", { order });
+    }
+  });
+
+  context.events.on("page-order:reorder", (detail: { pageNumbers: number[] }) => {
+    if (state) {
+      const reordered = reorderPages(state, detail.pageNumbers);
+      context.events.emit("page-order:reordered", { pages: reordered });
+    }
+  });
+
+  context.events.on("page-order:display-number", (detail: { actualPage: number }) => {
+    if (state) {
+      const displayPage = getDisplayPageNumber(state, detail.actualPage);
+      context.events.emit("page-order:display-page", { displayPage });
+    }
+  });
+}
 
 type PageOrderMode = "auto" | "japanese" | "western";
 
@@ -16,7 +52,6 @@ interface PageOrderState {
   totalPages: number;
 }
 
-// Detect page order based on filename patterns
 function detectPageOrder(pageNames: string[]): PageOrderMode {
   if (pageNames.length < 2) return "western";
 
@@ -62,15 +97,18 @@ function createPageOrderState(
 function setPageOrderMode(
   state: PageOrderState,
   mode: PageOrderMode,
+  context: ReaderContext,
 ): PageOrderState {
-  return {
-    ...state,
-    config: {
-      ...state.config,
-      mode,
-      userOverride: mode !== "auto",
-    },
+  state.config = {
+    ...state.config,
+    mode,
+    userOverride: mode !== "auto",
   };
+
+  const order = getPageOrder(state);
+  context.events.emit("page-order:changed", { mode, order });
+
+  return state;
 }
 
 function getPageOrder(state: PageOrderState): PageOrderMode {
@@ -101,4 +139,4 @@ function getDisplayPageNumber(
   }
 
   return actualPage;
-}
+}