Wire reactive islands end-to-end: live interactive demos on the demo page

- Rebuild sx-browser.js with signals spec module (was missing entirely)
- Register signal functions (signal, deref, effect, computed, etc.) as
  PRIMITIVES so runtime-evaluated SX code in island bodies can call them
- Add reactive deref detection in adapter-dom.sx: (deref sig) in island
  scope creates reactive-text node instead of static text
- Add Island SSR support in html.py (_render_island with data-sx-island)
- Add Island bundling in jinja_bridge.py (defisland defs sent to client)
- Update deps.py to track Island dependencies alongside Component
- Add defisland to _ASER_FORMS in async_eval.py
- Add clear-interval platform primitive (was missing)
- Create four live demo islands: counter, temperature, imperative, stopwatch

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

shared/sx/deps.py

@@ -10,7 +10,7 @@ from __future__ import annotations
 import os
 from typing import Any
 
-from .types import Component, Macro, Symbol
+from .types import Component, Island, Macro, Symbol
 
 
 def _use_ref() -> bool:
@@ -50,7 +50,7 @@ def _transitive_deps_fallback(name: str, env: dict[str, Any]) -> set[str]:
             return
         seen.add(n)
         val = env.get(n)
-        if isinstance(val, Component):
+        if isinstance(val, (Component, Island)):
             for dep in _scan_ast(val.body):
                 walk(dep)
         elif isinstance(val, Macro):
@@ -64,7 +64,7 @@ def _transitive_deps_fallback(name: str, env: dict[str, Any]) -> set[str]:
 
 def _compute_all_deps_fallback(env: dict[str, Any]) -> None:
     for key, val in env.items():
-        if isinstance(val, Component):
+        if isinstance(val, (Component, Island)):
             val.deps = _transitive_deps_fallback(key, env)
 
 
@@ -102,7 +102,7 @@ def _transitive_io_refs_fallback(
             return
         seen.add(n)
         val = env.get(n)
-        if isinstance(val, Component):
+        if isinstance(val, (Component, Island)):
             all_refs.update(_scan_io_refs_fallback(val.body, io_names))
             for dep in _scan_ast(val.body):
                 walk(dep)
@@ -120,7 +120,7 @@ def _compute_all_io_refs_fallback(
     env: dict[str, Any], io_names: set[str]
 ) -> None:
     for key, val in env.items():
-        if isinstance(val, Component):
+        if isinstance(val, (Component, Island)):
             val.io_refs = _transitive_io_refs_fallback(key, env, io_names)
 
 
@@ -135,7 +135,7 @@ def _components_needed_fallback(page_sx: str, env: dict[str, Any]) -> set[str]:
     for name in direct:
         all_needed.add(name)
         val = env.get(name)
-        if isinstance(val, Component) and val.deps:
+        if isinstance(val, (Component, Island)) and val.deps:
             all_needed.update(val.deps)
         else:
             all_needed.update(_transitive_deps_fallback(name, env))