fix: address code review issues and improve code quality

- Add owner_id check in repository delete operation
- Fix time range validation for partial updates
- Wrap pre-query in try/except for consistent error handling
- Use default_factory instead of mutable defaults
- Add max_length constraint for timezone field
- Remove unused dependencies and empty validators
- Extract magic numbers to constants
- Simplify update logic with model_dump

backend/src/v1/schedule_items/schemas.py

@@ -5,7 +5,7 @@ from enum import Enum
 from typing import ClassVar
 from uuid import UUID
 
-from pydantic import BaseModel, ConfigDict, Field, field_validator
+from pydantic import BaseModel, ConfigDict, Field
 
 
 class AttachmentType(str, Enum):
@@ -16,7 +16,7 @@ class AttachmentType(str, Enum):
 class ScheduleItemMetadataAttachment(BaseModel):
     name: str
     type: AttachmentType
-    visible_to: list[UUID] = []
+    visible_to: list[UUID] = Field(default_factory=list)
     url: str | None = None
     note: str | None = None
     content: str | None = None
@@ -26,7 +26,7 @@ class ScheduleItemMetadata(BaseModel):
     color: str | None = None
     location: str | None = None
     notes: str | None = None
-    attachments: list[ScheduleItemMetadataAttachment] = []
+    attachments: list[ScheduleItemMetadataAttachment] = Field(default_factory=list)
     version: int = 1
 
 
@@ -50,7 +50,7 @@ class ScheduleItemCreateRequest(BaseModel):
     description: str | None = Field(default=None, max_length=2000)
     start_at: datetime
     end_at: datetime | None = None
-    timezone: str = "UTC"
+    timezone: str = Field(default="UTC", max_length=50)
     metadata: ScheduleItemMetadata | None = None
 
 
@@ -61,15 +61,10 @@ class ScheduleItemUpdateRequest(BaseModel):
     description: str | None = Field(default=None, max_length=2000)
     start_at: datetime | None = None
     end_at: datetime | None = None
-    timezone: str | None = None
+    timezone: str | None = Field(default=None, max_length=50)
     metadata: ScheduleItemMetadata | None = None
     status: ScheduleItemStatus | None = None
 
-    @field_validator("end_at", mode="before")
-    @classmethod
-    def validate_end_at(cls, v: datetime | None, info) -> datetime | None:
-        return v
-
 
 class ScheduleItemResponse(BaseModel):
     model_config: ClassVar[ConfigDict] = ConfigDict(from_attributes=True)