Add Image models and clean up test code structure

Introduced `ImageCreate` and `Image` models to handle image-related data in the backend. Improved the organization and readability of the testing notebook by consolidating and formatting code into distinct sections with markdown cells.

backend/app/models.py

@@ -249,6 +249,17 @@ class Beamtime(Base):
     dewars = relationship("Dewar", back_populates="beamtime")
 
 
+class Image(Base):
+    __tablename__ = "images"
+
+    id = Column(Integer, primary_key=True, index=True, autoincrement=True)
+    pgroup = Column(String(255), nullable=False)
+    comment = Column(String(200), nullable=True)
+    filepath = Column(String(255), nullable=False)
+    status = Column(String(255), nullable=True)
+    sample_id = Column(Integer, ForeignKey("samples.id"), nullable=False)
+
+
 # class Results(Base):
 #    __tablename__ = "results"
 #