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/page-functions.sx

@@ -285,29 +285,30 @@
       (nil? slug)
       (quote (~specs/architecture-content))
       (let
-        ((found-spec (find-spec slug)))
+        ((found-spec (find-spec slug))
+          (filename
+            (if found-spec (get found-spec "filename") (str slug ".sx")))
+          (title (if found-spec (get found-spec "title") slug))
+          (desc (if found-spec (get found-spec "desc") "")))
         (if
-          (not found-spec)
-          (quasiquote (~specs/not-found :slug (unquote slug)))
-          (if
-            defname
-            (let
-              ((d (spec-explore-define (get found-spec "filename") defname)))
-              (if
-                d
-                (quasiquote
-                  (~specs-explorer/spec-explorer-define-detail
-                    :d (unquote d)
-                    :filename (unquote (get found-spec "filename"))))
-                (quasiquote
-                  (~specs/not-found :slug (unquote (str slug "." defname))))))
-            (let
-              ((data (spec-explore (get found-spec "filename") (get found-spec "title") (get found-spec "desc"))))
-              (if
-                data
-                (quasiquote
-                  (~specs-explorer/spec-explorer-content :data (unquote data)))
-                (quasiquote (~specs/not-found :slug (unquote slug)))))))))))
+          defname
+          (let
+            ((d (spec-explore-define filename defname)))
+            (if
+              d
+              (quasiquote
+                (~specs-explorer/spec-explorer-define-detail
+                  :d (unquote d)
+                  :filename (unquote filename)))
+              (quasiquote
+                (~specs/not-found :slug (unquote (str slug "." defname))))))
+          (let
+            ((data (spec-explore filename title desc)))
+            (if
+              data
+              (quasiquote
+                (~specs-explorer/spec-explorer-content :data (unquote data)))
+              (quasiquote (~specs/not-found :slug (unquote slug))))))))))
 
 (define
   make-spec-files