Fix reactive islands client-side navigation and hydration

Three bugs prevented islands from working during SX wire navigation:

1. components_for_request() only bundled Component and Macro defs, not
   Island defs — client never received defisland definitions during
   navigation (components_for_page for initial HTML shell was correct).

2. hydrate-island used morph-children which can't transfer addEventListener
   event handlers from freshly rendered DOM to existing nodes. Changed to
   clear+append so reactive DOM with live signal subscriptions is inserted
   directly.

3. asyncRenderToDom (client-side async page eval) checked _component but
   not _island on ~-prefixed names — islands fell through to generic eval
   which failed. Now delegates to renderDomIsland.

4. setInterval_/setTimeout_ passed SX Lambda objects directly to native
   timers. JS coerced them to "[object Object]" and tried to eval as code,
   causing "missing ] after element list". Added _wrapSxFn to convert SX
   lambdas to JS functions before passing to timers.

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

shared/sx/async_eval.py

@@ -45,7 +45,7 @@ import contextvars
 import inspect
 from typing import Any
 
-from .types import Component, Keyword, Lambda, Macro, NIL, Symbol
+from .types import Component, Island, Keyword, Lambda, Macro, NIL, Symbol
 
 # When True, _aser expands known components server-side instead of serializing
 # them for client rendering. Set during page slot evaluation so Python-only
@@ -1219,6 +1219,8 @@ async def _eval_slot_inner(
                 if isinstance(result, str):
                     return SxExpr(result)
                 return SxExpr(serialize(result))
+            elif isinstance(comp, Island):
+                pass  # Islands serialize as SX for client-side rendering
             else:
                 import logging
                 logging.getLogger("sx.eval").error(
@@ -1596,6 +1598,14 @@ async def _assf_define(expr, env, ctx):
     return NIL
 
 
+async def _assf_defisland(expr, env, ctx):
+    """Evaluate defisland AND serialize it — client needs the definition."""
+    import logging
+    logging.getLogger("sx.eval").info("_assf_defisland called for: %s", expr[1] if len(expr) > 1 else expr)
+    await async_eval(expr, env, ctx)
+    return serialize(expr)
+
+
 async def _assf_lambda(expr, env, ctx):
     return await _asf_lambda(expr, env, ctx)
 
@@ -1703,7 +1713,7 @@ _ASER_FORMS: dict[str, Any] = {
     "defcomp": _assf_define,
     "defmacro": _assf_define,
     "defhandler": _assf_define,
-    "defisland": _assf_define,
+    "defisland": _assf_defisland,
     "begin": _assf_begin,
     "do": _assf_begin,
     "quote": _assf_quote,