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>

events/sxc/pages/calendar.py

@@ -323,7 +323,7 @@ def _calendars_list_sx(ctx: dict, calendars: list) -> str:
         cal_name = getattr(cal, "name", "")
         href = prefix + url_for("calendar.get", calendar_slug=cal_slug)
         del_url = url_for("calendar.delete", calendar_slug=cal_slug)
-        csrf_hdr = f'{{"X-CSRFToken":"{csrf}"}}'
+        csrf_hdr = {"X-CSRFToken": csrf}
         parts.append(sx_call("crud-item",
                             href=href, name=cal_name, slug=cal_slug,
                             del_url=del_url, csrf_hdr=csrf_hdr,
@@ -656,7 +656,7 @@ def _markets_list_html(ctx: dict, markets: list) -> str:
         m_name = getattr(m, "name", "") if hasattr(m, "name") else m.get("name", "")
         market_href = call_url(ctx, "market_url", f"/{slug}/{m_slug}/")
         del_url = url_for("markets.delete_market", market_slug=m_slug)
-        csrf_hdr = f'{{"X-CSRFToken":"{csrf}"}}'
+        csrf_hdr = {"X-CSRFToken": csrf}
         parts.append(sx_call("crud-item",
                             href=market_href, name=m_name,
                             slug=m_slug, del_url=del_url,