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/bp/post/admin/routes.py

@@ -138,7 +138,7 @@ def _render_calendar_view(
                 e_id = getattr(e, "id", None)
                 e_name = esc(getattr(e, "name", ""))
                 t_url = toggle_url_fn(e_id)
-                hx_hdrs = f'{{"X-CSRFToken": "{csrf}"}}'
+                hx_hdrs = '{:X-CSRFToken "' + csrf + '"}'
 
                 if e_id in associated_entry_ids:
                     entry_btns.append(

blog/bp/post/routes.py

@@ -156,14 +156,10 @@ def register():
       csrf = generate_csrf_token()
 
       def _like_btn(liked):
-          if liked:
-              colour, icon, label = "text-red-600", "fa-solid fa-heart", "Unlike this post"
-          else:
-              colour, icon, label = "text-stone-300", "fa-regular fa-heart", "Like this post"
-          return sx_call("market-like-toggle-button",
-              colour=colour, action=like_url,
-              hx_headers=f'{{"X-CSRFToken": "{csrf}"}}',
-              label=label, icon_cls=icon)
+          return sx_call("blog-like-toggle",
+              like_url=like_url,
+              hx_headers={"X-CSRFToken": csrf},
+              heart="\u2764\ufe0f" if liked else "\U0001f90d")
 
       if not g.user:
           return sx_response(_like_btn(False), status=403)