feat(reader): add core infrastructure for feature-based architecture

- Add reader-context.ts: defines ReaderContext interface and factory
- Add reader-events.ts: event bus for feature communication
- Add reader-state.ts: centralized state management
- Add reader-navigation.ts: unified navigation and rendering API
- Add reader-services.ts: shared services (progress, chapters)
- Establishes foundation for Feature Registration Pattern

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

@@ -0,0 +1,45 @@
+import type { ReaderMetadata, ReaderState } from "./reader-context";
+
+type CurrentReader = import("./reader-context").CurrentReader;
+
+let currentState: ReaderState = {
+  currentReader: null,
+  readerMetadata: null,
+};
+
+export function getState(): ReaderState {
+  return { ...currentState };
+}
+
+export function setState(updates: Partial<ReaderState>): void {
+  const oldState = { ...currentState };
+  currentState = { ...currentState, ...updates };
+
+  // Emit events for significant changes
+  if (
+    updates.currentReader &&
+    oldState.currentReader !== updates.currentReader
+  ) {
+    readerEvents.emit("readerReady", currentState.currentReader);
+  }
+}
+
+export function getCurrentReader(): CurrentReader | null {
+  return currentState.currentReader;
+}
+
+export function getReaderMetadata(): ReaderMetadata | null {
+  return currentState.readerMetadata;
+}
+
+export function getCurrentPage(): number {
+  const reader = currentState.currentReader;
+  if (!reader) return 0;
+
+  if (reader.type === "ebook") {
+    return reader.currentSpineIndex;
+  }
+  return reader.currentPage;
+}
+
+import { readerEvents } from "./reader-events";