Lake demo: page path in copyright updates across navigation morphs

The ~sx-header island now shows the current page path (faded, after
the copyright) inside the copyright lake. Navigate between pages:
the path text updates via server-driven lake morph while the reactive
colour-cycling signal persists. Subtle visible proof of L2-3.

Also fixes Island &key param serialization in component-source helper.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sx/sxc/pages/helpers.py

@@ -44,7 +44,7 @@ def _component_source(name: str) -> str:
 
     comp = get_component_env().get(name)
     if isinstance(comp, Island):
-        param_strs = list(comp.params)
+        param_strs = (["&key"] + list(comp.params)) if comp.params else []
         if comp.has_children:
             param_strs.extend(["&rest", "children"])
         params_sx = "(" + " ".join(param_strs) + ")"