Fix examples.sx: paren balance + dict eval crash at startup

1. Extra closing paren in ex-tabs handler
2. tab-content dict values contained (div ...) HTML tags which crash
   during register_components since HTML primitives aren't in env

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

shared/sx/primitives.py

@@ -561,3 +561,15 @@ def prim_into(target: Any, coll: Any) -> Any:
         return result
     raise ValueError(f"into: unsupported target type {type(target).__name__}")
 
+
+@register_primitive("random-int")
+def prim_random_int(low: int, high: int) -> int:
+    import random
+    return random.randint(int(low), int(high))
+
+
+@register_primitive("json-encode")
+def prim_json_encode(value) -> str:
+    import json
+    return json.dumps(value, indent=2)
+