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/models.py

@@ -153,4 +153,47 @@ class ReadingProgress(models.Model):
             "current_position", "last_page",
             "device_id", "device_name", "version", "updated_at",
         ])
-        return self, True
+        return self, True
+
+
+class ReadingSchedule(models.Model):
+    """A reading schedule that groups sections into weekly meetings for an ebook."""
+
+    ebook = models.ForeignKey(EBook, on_delete=models.CASCADE, related_name="schedules")
+    user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name="schedules")
+    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)
+
+    class Meta:
+        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"])]
+
+    def __str__(self):
+        return f"Schedule for {self.ebook.title} ({self.meeting_count} meetings)"
+
+
+class MeetingSection(models.Model):
+    """A single meeting within a reading schedule, containing assigned chapters."""
+
+    schedule = models.ForeignKey(ReadingSchedule, on_delete=models.CASCADE, related_name="meetings")
+    meeting_index = models.PositiveIntegerField()
+    title = models.CharField(max_length=256, default="Meeting")
+    estimated_time_minutes = models.PositiveIntegerField(default=0)
+    chapter_ids = models.JSONField(default=list)
+
+    class Meta:
+        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"])]
+
+    def __str__(self):
+        return f"Meeting {self.meeting_index + 1}: {self.title}"