Implement 7 missing sx attributes: boost, preload, preserve, indicator, validate, ignore, optimistic

Add sx-preserve/sx-ignore (morph skip), sx-indicator (loading element),
sx-validate (form validation), sx-boost (progressive enhancement),
sx-preload (hover prefetch with 30s cache), and sx-optimistic (instant
UI preview with rollback). Move all from HTMX_MISSING_ATTRS to
SX_UNIQUE_ATTRS with full ATTR_DETAILS docs and reference.sx demos.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sx/sxc/sx_components.py

@@ -579,21 +579,19 @@ def _reference_attr_detail_sx(slug: str) -> str:
 
 
 async def _reference_attrs_sx() -> str:
-    from content.pages import REQUEST_ATTRS, BEHAVIOR_ATTRS, SX_UNIQUE_ATTRS, HTMX_MISSING_ATTRS
+    from content.pages import REQUEST_ATTRS, BEHAVIOR_ATTRS, SX_UNIQUE_ATTRS
     req = await _attr_table_sx("Request Attributes", REQUEST_ATTRS)
     beh = await _attr_table_sx("Behavior Attributes", BEHAVIOR_ATTRS)
     uniq = await _attr_table_sx("Unique to sx", SX_UNIQUE_ATTRS)
-    missing = await _attr_table_sx("htmx features not yet in sx", HTMX_MISSING_ATTRS)
     return (
         f'(~doc-page :title "Attribute Reference"'
         f'  (p :class "text-stone-600 mb-6"'
-        f'    "sx attributes mirror htmx where possible. This table shows what exists, '
-        f'what\'s unique to sx, and what\'s not yet implemented.")'
+        f'    "sx attributes mirror htmx where possible. This table shows all '
+        f'available attributes and their status.")'
         f'  (div :class "space-y-8"'
         f'    {req}'
         f'    {beh}'
-        f'    {uniq}'
-        f'    {missing}))'
+        f'    {uniq}))'
     )