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>

market/sxc/pages/helpers.py

@@ -129,7 +129,7 @@ async def _h_page_admin_data(slug=None, **kw) -> dict:
         m_name = getattr(m, "name", "") or (m.get("name", "") if isinstance(m, dict) else "")
         href = prefix + f"/{post_slug}/{m_slug}/"
         del_url = url_for("page_admin.delete_market", market_slug=m_slug)
-        csrf_hdr = f'{{"X-CSRFToken":"{csrf}"}}'
+        csrf_hdr = {"X-CSRFToken": csrf}
         markets.append({
             "href": href, "name": m_name, "slug": m_slug,
             "del-url": del_url, "csrf-hdr": csrf_hdr,

market/sxc/pages/renders.py

@@ -189,7 +189,7 @@ def render_like_toggle_button(slug: str, liked: bool, *,
     return sx_call(
         "market-like-toggle-button",
         colour=colour, action=like_url,
-        hx_headers=f'{{"X-CSRFToken": "{csrf}"}}',
+        hx_headers={"X-CSRFToken": csrf},
         label=label, icon_cls=icon,
     )