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>

web/adapter-sx.sx

@@ -437,17 +437,9 @@
         (let
           ((f (trampoline (eval-expr (first args) env)))
             (coll (trampoline (eval-expr (nth args 1) env))))
-          (map
-            (fn
-              (item)
-              (if
-                (lambda? f)
-                (let
-                  ((local (env-merge (lambda-closure f) env)))
-                  (env-bind! local (first (lambda-params f)) item)
-                  (aser (lambda-body f) local))
-                (cek-call f (list item))))
-            coll))
+          (let
+            ((results (map (fn (item) (if (lambda? f) (let ((local (env-extend (lambda-closure f)))) (env-bind! local (first (lambda-params f)) item) (aser (lambda-body f) local)) (cek-call f (list item)))) coll)))
+            (aser-fragment results env)))
         (= name "map-indexed")
         (let
           ((f (trampoline (eval-expr (first args) env)))