feat(compiler): add island marker codegen and props contract

Emits the data-wrn-island placeholder, parses client:* strategies, and
rejects non-serializable props at compile time via WRN-ISLAND-PROPS so
the serialization boundary fails where it is cheapest to fix.

Island names become URL path segments when the browser fetches the
island bundle, so they are validated with core's existing
isSafeIslandName rather than relying on escaping alone. This adds
@wrnexus/core to the compiler's dependencies; core has no dependencies
of its own, so no cycle is introduced.

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

packages/compiler/package.json

@@ -7,9 +7,10 @@
     ".": "./src/index.ts"
   },
   "dependencies": {
+    "@wrnexus/core": "workspace:*",
     "@wrnexus/csr": "workspace:*",
-    "@wrnexus/syntax": "workspace:*",
     "@wrnexus/store": "workspace:*",
+    "@wrnexus/syntax": "workspace:*",
     "@wrnexus/validation": "workspace:*"
   }
 }