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/admin.sx

@@ -206,7 +206,7 @@
                 (when is-admin
                   (~blog-snippet-visibility-select
                     :patch-url (get s "patch_url")
-                    :hx-headers (str "{\"X-CSRFToken\": \"" csrf "\"}")
+                    :hx-headers {:X-CSRFToken csrf}
                     :options (<>
                       (~blog-snippet-option :value "private" :selected (= vis "private") :label "private")
                       (~blog-snippet-option :value "shared" :selected (= vis "shared") :label "shared")
@@ -217,7 +217,7 @@
                     :trigger-target "#snippets-list"
                     :title "Delete snippet?"
                     :text (str "Delete \u201c" name "\u201d?")
-                    :sx-headers (str "{\"X-CSRFToken\": \"" csrf "\"}")
+                    :sx-headers {:X-CSRFToken csrf}
                     :cls "px-3 py-1 text-sm bg-red-200 hover:bg-red-300 rounded text-red-800 flex-shrink-0"))))))
           (or snippets (list)))))))
 
@@ -240,7 +240,7 @@
             :edit-url (get mi "edit_url")
             :delete-url (get mi "delete_url")
             :confirm-text (str "Remove " (get mi "label") " from the menu?")
-            :hx-headers (str "{\"X-CSRFToken\": \"" csrf "\"}")))
+            :hx-headers {:X-CSRFToken csrf}))
           (or menu-items (list)))))))
 
 ;; Tag Groups — receives serialized tag group data from service