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>

shared/static/scripts/sx.js

@@ -251,6 +251,18 @@
     return results;
   }
 
+  /** Serialize a JS object as SX dict {:key "val" ...} for attribute values. */
+  function _serializeDict(obj) {
+    var parts = [];
+    for (var k in obj) {
+      if (!obj.hasOwnProperty(k)) continue;
+      var v = obj[k];
+      var vs = typeof v === "string" ? '"' + v.replace(/\\/g, "\\\\").replace(/"/g, '\\"') + '"' : String(v);
+      parts.push(":" + k + " " + vs);
+    }
+    return "{" + parts.join(" ") + "}";
+  }
+
   // --- Primitives ---
 
   var PRIMITIVES = {};
@@ -1420,7 +1432,7 @@
         } else if (attrVal === true) {
           el.setAttribute(attrName, "");
         } else {
-          el.setAttribute(attrName, String(attrVal));
+          el.setAttribute(attrName, typeof attrVal === "object" && attrVal !== null && !Array.isArray(attrVal) ? _serializeDict(attrVal) : String(attrVal));
         }
       } else {
         // Child
@@ -1851,7 +1863,7 @@
             cancelButtonText: "Cancel"
           }).then(function (result) {
             if (!result.isConfirmed) return;
-            return _doFetch(el, method, url, extraParams);
+            return _doFetch(el, verbInfo, method, url, extraParams);
           });
         }
         if (!window.confirm(confirmMsg)) return Promise.resolve();
@@ -1866,10 +1878,10 @@
         extraParams.promptValue = promptVal;
       }
 
-      return _doFetch(el, method, url, extraParams);
+      return _doFetch(el, verbInfo, method, url, extraParams);
     }
 
-    function _doFetch(el, method, url, extraParams) {
+    function _doFetch(el, verbInfo, method, url, extraParams) {
       // sx-sync: abort previous
       var sync = el.getAttribute("sx-sync");
       if (sync && sync.indexOf("replace") >= 0) abortPrevious(el);
@@ -1895,12 +1907,12 @@
       var cssHeader = _getSxCssHeader();
       if (cssHeader) headers["SX-Css"] = cssHeader;
 
-      // Extra headers from sx-headers
+      // Extra headers from sx-headers (SX dict {:key "val"} or JSON)
       var extraH = el.getAttribute("sx-headers");
       if (extraH) {
         try {
-          var parsed = JSON.parse(extraH);
-          for (var k in parsed) headers[k] = parsed[k];
+          var parsed = extraH.charAt(0) === "{" && extraH.charAt(1) === ":" ? parse(extraH) : JSON.parse(extraH);
+          for (var k in parsed) headers[k] = String(parsed[k]);
         } catch (e) { /* ignore */ }
       }
 
@@ -1974,7 +1986,7 @@
       var valsAttr = el.getAttribute("sx-vals");
       if (valsAttr) {
         try {
-          var vals = JSON.parse(valsAttr);
+          var vals = valsAttr.charAt(0) === "{" && valsAttr.charAt(1) === ":" ? parse(valsAttr) : JSON.parse(valsAttr);
           if (method === "GET") {
             for (var vk in vals) {
               url += (url.indexOf("?") >= 0 ? "&" : "?") + encodeURIComponent(vk) + "=" + encodeURIComponent(vals[vk]);