Add inline block editing to schedule templates

- Backend: PATCH /api/schedules/{template_id}/blocks/{block_id} endpoint
- Frontend: Edit button on each block row expands an inline form
  pre-filled with current subject, times, and label; saves via PATCH

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/schemas/schedule.py

@@ -11,6 +11,15 @@ class ScheduleBlockCreate(BaseModel):
     order_index: int = 0
 
 
+class ScheduleBlockUpdate(BaseModel):
+    subject_id: int | None = None
+    time_start: time | None = None
+    time_end: time | None = None
+    label: str | None = None
+    notes: str | None = None
+    order_index: int | None = None
+
+
 class ScheduleBlockOut(BaseModel):
     id: int
     subject_id: int | None