Bootstrap stores + event bridge, add island hydration to boot.sx

- signals.sx: fix has? → has-key?, add def-store/use-store/clear-stores
  (L3 named stores), emit-event/on-event/bridge-event (event bridge)
- boot.sx: add sx-hydrate-islands, hydrate-island, dispose-island
  for client-side island hydration from SSR output
- bootstrap_js.py: add RENAMES, platform fns (domListen, eventDetail,
  domGetData, jsonParse), public API exports for all new functions
- bootstrap_py.py: add RENAMES, server-side no-op stubs for DOM events
- Regenerate sx-ref.js (with boot adapter) and sx_ref.py
- Update reactive-islands status: hydration, stores, bridge all spec'd

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

shared/sx/ref/bootstrap_py.py

@@ -174,6 +174,16 @@ class PyEmitter:
             "*batch-depth*": "_batch_depth",
             "*batch-queue*": "_batch_queue",
             "*island-scope*": "_island_scope",
+            "*store-registry*": "_store_registry",
+            "def-store": "def_store",
+            "use-store": "use_store",
+            "clear-stores": "clear_stores",
+            "emit-event": "emit_event",
+            "on-event": "on_event",
+            "bridge-event": "bridge_event",
+            "dom-listen": "dom_listen",
+            "dom-dispatch": "dom_dispatch",
+            "event-detail": "event_detail",
             "macro?": "is_macro",
             "primitive?": "is_primitive",
             "get-primitive": "get_primitive",
@@ -1544,6 +1554,17 @@ def is_empty_dict(d):
     return len(d) == 0
 
 
+# DOM event primitives — no-ops on server (browser-only).
+def dom_listen(el, name, handler):
+    return lambda: None
+
+def dom_dispatch(el, name, detail=None):
+    return False
+
+def event_detail(e):
+    return None
+
+
 def env_has(env, name):
     return name in env