fix(web,api): lecteur — worker pdf.js dédié, shell commun et préférences par livre

Régression worker PDF : le worker pdf.js est désormais instancié une
seule fois via un port dédié (?worker&url) et reconfiguré à chaque
montage, au lieu d'un workerSrc recalculé qui cassait le rendu.

- ReaderShell : chrome commun aux lecteurs (toolbar, zones de tap,
  statut) et contrat ReaderControls pour EPUB/PDF/CBZ
- préférences de lecture par livre (mode horizontal/vertical, fit) :
  table reader_preferences + migrations idempotentes, module API,
  DTO partagés, client web avec fallback localStorage hors-ligne

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/api/src/reader/reader-preferences.service.ts

@@ -0,0 +1,47 @@
+import { Injectable, NotFoundException } from "@nestjs/common";
+import { eq, sql } from "drizzle-orm";
+import { UpdateReaderPreferencesDto } from "@readabook/shared";
+import { DatabaseService } from "../database/database.service.js";
+import { books, readerPreferences } from "../database/schema.js";
+
+@Injectable()
+export class ReaderPreferencesService {
+  constructor(private readonly database: DatabaseService) {}
+
+  find(userId: number, bookId: number) {
+    const row = this.database.db
+      .select({
+        mode: readerPreferences.mode,
+        fit: readerPreferences.fit,
+        updatedAt: readerPreferences.updatedAt
+      })
+      .from(readerPreferences)
+      .where(sql`${readerPreferences.userId} = ${userId} AND ${readerPreferences.bookId} = ${bookId}`)
+      .get();
+    return row ?? { mode: "paged", fit: null };
+  }
+
+  upsert(userId: number, bookId: number, input: UpdateReaderPreferencesDto) {
+    const book = this.database.db.select({ id: books.id }).from(books).where(eq(books.id, bookId)).get();
+    if (!book) throw new NotFoundException("Book not found");
+
+    const current = this.find(userId, bookId);
+    const now = this.database.now();
+    const mode = input.mode ?? current.mode;
+    const fit = input.fit === undefined ? current.fit : input.fit;
+
+    this.database.sqlite
+      .prepare(
+        `
+        INSERT INTO reader_preferences(user_id, book_id, mode, fit, created_at, updated_at)
+        VALUES (?, ?, ?, ?, ?, ?)
+        ON CONFLICT(user_id, book_id) DO UPDATE SET
+          mode = excluded.mode,
+          fit = excluded.fit,
+          updated_at = excluded.updated_at
+      `
+      )
+      .run(userId, bookId, mode, fit, now, now);
+    return this.find(userId, bookId);
+  }
+}