feat(islands): wire islands end to end

The island pieces existed but nothing connected .wrn compilation to island
emission. Now:

- codegen emits a data-wrn-island placeholder for component tags bound to
  .tsx imports, keeping .wrn components on the normal mount path
- the dev pipeline and static build resolve island imports, thread the
  names into codegen, and build the bundles
- collectScripts adds /__wrnexus/islands.js only when island markup is
  present, so island-free pages still ship nothing
- island routes classify as static-interactive via hasIslands

Three bugs found by driving a real page in the browser:

1. The mount runtime was never built anywhere, so the bootstrap 404'd and
   no island mounted.
2. Building the runtime separately from the islands gave each its own copy
   of React: "Cannot read properties of null (reading 'useState')". The
   runtime is now an entrypoint of the same build so React stays in one
   shared chunk. The existing single-React test only compared bundles
   within one build and could not see across build boundaries.
3. Island props arrived as attribute strings, so start={3} was "3" and
   incrementing produced "31" then "311". Props now follow JSX semantics:
   {…} parses as JSON, quoted values stay strings, and a runtime
   expression is a WRN-ISLAND-PROPS build error rather than a silent
   wrong value.

island-codegen.ts no longer imports @wrnexus/core. Compiler modules are
bundled into the Node-only VS Code extension, which contains no other
packages, so a runtime import of core broke the editor compiler; the two
helpers are implemented locally and the core dependency is dropped again.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/react/src/browser.ts

@@ -0,0 +1,8 @@
+/**
+ * Browser entry for the island mount runtime, served at
+ * `/__wrnexus/island/runtime.js` and imported by the bootstrap only when a
+ * `data-wrn-island` marker is present.
+ */
+export { islandRootCount, mountIslands, remountIslands, unmountIslands } from "./island-runtime.ts";
+export type { MountOptions } from "./island-runtime.ts";
+export { setStoreResolver, useWrnActions, useWrnStore } from "./store-bridge.ts";

packages/react/src/error-boundary.tsx

@@ -41,4 +41,4 @@ export class IslandErrorBoundary extends Component<
       </div>
     );
   }
-}
+}