refactor: update sleep session logic, models, and agent protocols

backend/app/models.py

@@ -9,6 +9,5 @@ class SleepSession(SQLModel, table=True):
     id: Optional[int] = Field(default=None, primary_key=True)
     start_time: datetime = Field(nullable=False)
     end_time: Optional[datetime] = Field(default=None, nullable=True)
-    notes: Optional[str] = Field(default=None)
     created_at: datetime = Field(default_factory=lambda: datetime.now(timezone.utc))
     updated_at: datetime = Field(default_factory=lambda: datetime.now(timezone.utc))

backend/app/schemas.py

@@ -6,22 +6,17 @@ from pydantic import BaseModel
 class SleepSessionCreate(BaseModel):
     start_time: datetime
 
-
 class SleepSessionUpdate(BaseModel):
     start_time: Optional[datetime] = None
     end_time: Optional[datetime] = None
-    notes: Optional[str] = None
-
 
 class SleepSessionRead(BaseModel):
     id: int
     start_time: datetime
     end_time: Optional[datetime]
-    notes: Optional[str]
     created_at: datetime
     updated_at: datetime
 
-
 class SessionListResponse(BaseModel):
     sessions: List[SleepSessionRead]
     total: int