fix(e2e): restore observer-node coordinates in seed

A flake8 B007 fix at commit time renamed the whole observer-specs tuple
to (_area, _lat, _lon), but the Node() call below still referenced lat/lon.
Those names then resolved to the leaked values from the preceding
content_specs loop (last iteration = Delta's None/None), so all observer
nodes were seeded without coordinates and dropped from the map (7 -> 3
markers). Underscore only `area` (genuinely unused in that loop); lat/lon
are used in Node(), so they stay as loop vars.

e2e/seed_data.py

@@ -121,7 +121,7 @@ def seed_nodes(session: Session) -> dict[str, Node]:
         session.add(node)
         nodes[pk] = node
 
-    for i, (pk, name, _area, _lat, _lon) in enumerate(observer_specs):
+    for i, (pk, name, _area, lat, lon) in enumerate(observer_specs):
         node = Node(
             public_key=pk,
             name=name,