Spec explorer: fix SxExpr rendering bugs, add drill-in UX, Playwright tests

Fix 3 OCaml bugs that caused spec explorer to hang:
- sx_types: inspect outputs quoted string for SxExpr (not bare symbol)
- sx_primitives: serialize/to_string extract SxExpr/RawHTML content
- sx_render: handle SxExpr in both render-to-html paths

Restructure spec explorer for performance:
- Lightweight overview: name + kind only (was full source for 141 defs)
- Drill-in detail: click definition → params, effects, signature
- explore() page function accepts optional second arg for drill-in
- spec() passes through non-string slugs from nested routing

Fix aser map result wrapping:
- aser-special map now wraps results in fragment (<> ...) via aser-fragment
- Prevents ((div ...) (div ...)) nested lists that caused client "Not callable"

5 Playwright tests: overview load, no errors, SPA nav, drill-in detail+params

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

sx/sx/page-functions.sx

@@ -213,10 +213,12 @@
   spec
   (fn
     (slug)
-    (if
+    (cond
       (nil? slug)
       (quote (~specs/architecture-content))
-      (case
+      (not (= (type-of slug) "string"))
+      slug
+      :else (case
         slug
         "core"
         (let
@@ -278,22 +280,34 @@
 (define
   explore
   (fn
-    (slug)
+    (slug defname)
     (if
       (nil? slug)
       (quote (~specs/architecture-content))
       (let
         ((found-spec (find-spec slug)))
         (if
-          found-spec
-          (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)))))
-          (quasiquote (~specs/not-found :slug (unquote slug))))))))
+          (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)))))))))))
 
 (define
   make-spec-files