feat: Implement image thumbnail generation, storage, and API endpoints for assets, including a regeneration utility.

models/Asset.py

@@ -18,6 +18,7 @@ class Asset(BaseModel):
     data: Optional[bytes] = None
     tg_doc_file_id: Optional[str] = None
     tg_photo_file_id: Optional[str] = None
+    thumbnail: Optional[bytes] = None
     tags: List[str] = []
     created_at: datetime = Field(default_factory=lambda: datetime.now(UTC))
     updated_at: datetime = Field(default_factory=lambda: datetime.now(UTC))