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>

account/bp/account/routes.py

@@ -69,7 +69,7 @@ def register(url_prefix="/"):
         return sx_response(sx_call(
             "account-newsletter-toggle",
             id=f"nl-{nid}", url=toggle_url,
-            hdrs=f'{{"X-CSRFToken": "{csrf}"}}',
+            hdrs={"X-CSRFToken": csrf},
             target=f"#nl-{nid}",
             cls=f"relative inline-flex h-6 w-11 items-center rounded-full transition-colors focus:outline-none focus:ring-2 focus:ring-emerald-500 focus:ring-offset-2 {bg}",
             checked=checked,

account/sx/newsletters.sx

@@ -54,7 +54,7 @@
                 :toggle (~account-newsletter-toggle
                   :id (str "nl-" nid)
                   :url toggle-url
-                  :hdrs (str "{\"X-CSRFToken\": \"" csrf "\"}")
+                  :hdrs {:X-CSRFToken csrf}
                   :target (str "#nl-" nid)
                   :cls (str "relative inline-flex h-6 w-11 items-center rounded-full transition-colors focus:outline-none focus:ring-2 focus:ring-emerald-500 focus:ring-offset-2 " bg)
                   :checked checked