Migrate remaining 7 ref endpoints to SX, add :returns type annotations

Add 14 new IO primitives to boundary.sx: web interop (request-form,
request-json, request-header, request-content-type, request-args-all,
request-form-all, request-headers-all, request-file-name), response
manipulation (set-response-header, set-response-status), ephemeral
state (state-get, state-set!), and timing (now, sleep).

All 19 reference handlers now have :returns type annotations using
types.sx vocabulary. Response meta (headers/status) flows through
context vars, applied by register_route_handlers after execution.

Only SSE endpoint remains in Python (async generator paradigm).

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

shared/sx/handlers.py

@@ -239,10 +239,19 @@ def register_route_handlers(app_or_bp: Any, service_name: str) -> int:
 
         async def _route_view(_h=_hdef, **path_kwargs):
             from shared.sx.helpers import sx_response
+            from shared.sx.primitives_io import reset_response_meta, get_response_meta
+            reset_response_meta()
             args = dict(request.args)
             args.update(path_kwargs)
             result = await execute_handler(_h, service_name, args=args)
-            return sx_response(result)
+            resp = sx_response(result)
+            meta = get_response_meta()
+            if meta:
+                if meta.get("status"):
+                    resp.status_code = meta["status"]
+                for k, v in meta.get("headers", {}).items():
+                    resp.headers[k] = v
+            return resp
 
         endpoint = f"sx_route_{name}"
         view_fn = _route_view