test(islands): guard zero-JS routes and single-React bundling

Two guards protect the core promise: a route with no islands emits no
assets at all, and a page with several islands keeps React in one shared
chunk.

buildIslands now writes a generated entry per island instead of passing
component sources directly. Two islands sharing a source deduped to a
single entrypoint, and output order is not guaranteed to match input
order, so island names could bind to the wrong bundle.

Island modules are excluded from the editor compiler bundle: it globs
packages/compiler/src, and island-bundle.ts calls Bun.build while
island-codegen.ts imports @wrnexus/core — neither belongs in a Node-only
VS Code artifact.

Integration assertions share one build. bun test interferes with
Bun.build's module reads after several build calls in one process, while
the same calls succeed repeatedly outside the runner; production is
unaffected.

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

docs/public-api-0.8.json

@@ -2259,6 +2259,30 @@
         "subjectQueue"
       ]
     },
+    "@wrnexus/react": {
+      ".": [
+        "BoundStore",
+        "IslandErrorBoundary",
+        "IslandErrorBoundaryProps",
+        "IslandStore",
+        "MountOptions",
+        "SnapshotCache",
+        "SnapshotSource",
+        "StoreResolver",
+        "createSelectorCache",
+        "createSnapshotCache",
+        "islandRootCount",
+        "mountIslands",
+        "remountIslands",
+        "setStoreResolver",
+        "unmountIslands",
+        "useWrnActions",
+        "useWrnStore"
+      ],
+      "./runtime": [
+        "getIslandRuntime"
+      ]
+    },
     "@wrnexus/reactive": {
       ".": [
         "AnimationTimeline",