Merge main into macros: resolve nav restructure conflicts

Take HEAD's updated typed-sx content (deftype, effect system details)
with main's /etc/plans/ path prefix. Take main's newer sx-browser.js
timestamp.

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

shared/sx/ref/sx_ref.py

@@ -1192,6 +1192,7 @@ def eval_expr(expr, env):
         elif sx_truthy((name == 'nil')):
             return NIL
         else:
+            debug_log('Undefined symbol:', name, 'primitive?:', is_primitive(name))
             return error(sx_str('Undefined symbol: ', name))
     elif _match == 'keyword':
         return keyword_name(expr)