Replace JSON sx-headers with SX dict expressions, fix blog like component

sx-headers attributes now use native SX dict format {:key val} instead of
JSON strings. Eliminates manual JSON string construction in both .sx files
and Python callers.

- sx.js: parse sx-headers/sx-vals as SX dict ({: prefix) with JSON fallback,
  add _serializeDict for dict→attribute serialization, fix verbInfo scope in
  _doFetch error handler
- html.py: serialize dict attribute values via SX serialize() not str()
- All .sx files: {:X-CSRFToken csrf} replaces (str "{\"X-CSRFToken\": ...}")
- All Python callers: {"X-CSRFToken": csrf} dict replaces f-string JSON
- Blog like: extract ~blog-like-toggle, fix POST returning wrong component,
  fix emoji escapes in .sx (parser has no \U support), fix card :hx-headers
  keyword mismatch, wrap sx_content in SxExpr for evaluation

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

blog/sx/settings.sx

@@ -2,7 +2,7 @@
 
 (defcomp ~blog-features-form (&key features-url calendar-checked market-checked hs-trigger)
   (form :sx-put features-url :sx-target "#features-panel" :sx-swap "outerHTML"
-    :sx-headers "{\"Content-Type\": \"application/json\"}" :sx-encoding "json" :class "space-y-3"
+    :sx-headers {:Content-Type "application/json"} :sx-encoding "json" :class "space-y-3"
     (label :class "flex items-center gap-3 cursor-pointer"
       (input :type "checkbox" :name "calendar" :value "true" :checked calendar-checked
         :class "h-5 w-5 rounded border-stone-300 text-blue-600 focus:ring-blue-500"
@@ -140,7 +140,7 @@
           (~blog-associated-entry
             :confirm-text (get e "confirm_text")
             :toggle-url (get e "toggle_url")
-            :hx-headers (str "{\"X-CSRFToken\": \"" csrf "\"}")
+            :hx-headers {:X-CSRFToken csrf}
             :img (~blog-entry-image :src (get e "cal_image") :title (get e "cal_title"))
             :name (get e "name")
             :date-str (get e "date_str")))