Spec explorer: full source in drill-in, explore any .sx file

- spec-explore-define uses serialize (full body) instead of signature
- _spec-search-dirs expanded: spec/, web/, lib/, shared/sx/ref/, sx/, sxc/, shared/sx/templates/
- explore() works with any filename, not just nav spec items
- Playwright tests use flexible regex for line/define counts

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

sx/sx/data/helpers.sx

@@ -59,7 +59,9 @@
               (parts (append parts (list params body))))
             (pretty-print parts)))))))
 
-(define _spec-dirs (list "spec" "web" "shared/sx/ref" "lib"))
+(define
+  _spec-dirs
+  (list "spec" "web" "shared/sx/ref" "lib" "sx" "sxc" "shared/sx/templates"))
 
 (define
   read-spec-file
@@ -95,7 +97,14 @@
   _spec-search-dirs
   (fn
     ()
-    (list _spec-dir _web-dir _lib-dir (str _project-dir "/shared/sx/ref"))))
+    (list
+      _spec-dir
+      _web-dir
+      _lib-dir
+      (str _project-dir "/shared/sx/ref")
+      (str _project-dir "/sx")
+      (str _project-dir "/sxc")
+      (str _project-dir "/shared/sx/templates"))))
 
 (define
   read-spec-file