feat: US #32 Section-based Reading Recommendations

Backend:
- Add ReadingSchedule and MeetingSection models for ebook reading schedules
- Implement recommendation algorithm: greedy partition minimizing per-meeting time variance
- Algorithm respects chapter boundaries, estimates time based on chapter weight
- Add serializers for schedules (list/detail/generate/confirm/update)
- Add ScheduleViewSet with endpoints: list, create (generate), retrieve, regenerate, confirm, update_meeting, reorder_meetings
- Add URL routes for /api/books/schedules/
- Create migration 0004 for new models

Frontend:
- Add types: MeetingSection, ReadingSchedule, GenerateRecommendationsRequest
- Add schedulesApi with methods: getSchedules, generateRecommendations, confirmSchedule, updateMeeting, reorderMeetings, deleteSchedule
- Build RecommendationPage with 4-column meeting layout, drag-and-drop chapter reassignment, generate/regenerate/confirm flow
- Add 'Schedule Reading' menu item to BookContextMenu
- Add route: /books/:ebookId/schedule

backend/apps/books/migrations/0004_add_reading_schedule.py

@@ -0,0 +1,52 @@
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("books", "0003_readingprogress_epub_location"),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="ReadingSchedule",
+            fields=[
+                ("id", models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name="ID")),
+                ("meeting_count", models.PositiveIntegerField(default=4)),
+                ("confirmed", models.BooleanField(default=False)),
+                ("created_at", models.DateTimeField(auto_now_add=True)),
+                ("updated_at", models.DateTimeField(auto_now=True)),
+                ("ebook", models.ForeignKey(on_delete=models.CASCADE, related_name="schedules", to="books.ebook")),
+                ("user", models.ForeignKey(on_delete=models.CASCADE, related_name="schedules", to=settings.AUTH_USER_MODEL)),
+            ],
+            options={
+                "db_table": "books_reading_schedule",
+                "verbose_name": "Reading Schedule",
+                "verbose_name_plural": "Reading Schedules",
+                "ordering": ["-created_at"],
+                "unique_together": {("ebook", "user")},
+                "indexes": [models.Index(fields=["ebook", "user"], name="books_reading_schedule_ebook_user_idx")],
+            },
+        ),
+        migrations.CreateModel(
+            name="MeetingSection",
+            fields=[
+                ("id", models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name="ID")),
+                ("meeting_index", models.PositiveIntegerField()),
+                ("title", models.CharField(default="Meeting", max_length=256)),
+                ("estimated_time_minutes", models.PositiveIntegerField(default=0)),
+                ("chapter_ids", models.JSONField(default=list)),
+                ("schedule", models.ForeignKey(on_delete=models.CASCADE, related_name="meetings", to="books.readingschedule")),
+            ],
+            options={
+                "db_table": "books_meeting_section",
+                "verbose_name": "Meeting Section",
+                "verbose_name_plural": "Meeting Sections",
+                "ordering": ["meeting_index"],
+                "unique_together": {("schedule", "meeting_index")},
+                "indexes": [models.Index(fields=["schedule", "meeting_index"], name="books_meeting_section_schedule_meeting_idx")],
+            },
+        ),
+    ]