Making objective_lens a thing

app/models/scope_info.py

@@ -27,6 +27,11 @@ class ScopeInfo(Base):
     model_suffix: Mapped[str | None] = mapped_column(
         String, nullable=True, default=None
     )
+    # The lens diameter is a descriptive attribute (the "50" in "3-18x50"), not a
+    # connection dimension — it has no AttachmentPoint.
+    objective_lens_diameter_mm: Mapped[float | None] = mapped_column(
+        Float, nullable=True, default=None
+    )
     # Kept as the raw string from the sheet (e.g. "0.75", "1/16") so no precision
     # or notation is lost; the parsed thread lives on its own AttachmentPoint.
     objective_thread_pitch: Mapped[str | None] = mapped_column(