Fix bootstrapper dict literal transpilation: emit values through emit()

The SX parser produces native Python dicts for {:key val} syntax, but
both JSEmitter and PyEmitter had no dict case in emit() — falling through
to str(expr) which output raw AST. This broke client-side routing because
process-page-scripts used {"parsed" (parse-route-pattern ...)} and the
function call was emitted as a JS array of Symbols instead of an actual
function call.

Add _emit_native_dict() to both bootstrappers + 8 unit tests.

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

shared/sx/ref/bootstrap_py.py

@@ -52,6 +52,8 @@ class PyEmitter:
             return self._emit_symbol(expr.name)
         if isinstance(expr, Keyword):
             return self._py_string(expr.name)
+        if isinstance(expr, dict):
+            return self._emit_native_dict(expr)
         if isinstance(expr, list):
             return self._emit_list(expr)
         return str(expr)
@@ -526,6 +528,13 @@ class PyEmitter:
         parts = [self.emit(e) for e in exprs]
         return "_sx_begin(" + ", ".join(parts) + ")"
 
+    def _emit_native_dict(self, expr: dict) -> str:
+        """Emit a native Python dict (from parser's {:key val} syntax)."""
+        parts = []
+        for key, val in expr.items():
+            parts.append(f"{self._py_string(key)}: {self.emit(val)}")
+        return "{" + ", ".join(parts) + "}"
+
     def _emit_dict_literal(self, expr) -> str:
         pairs = expr[1:]
         parts = []