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>

docs/public-api-0.8.json

@@ -973,6 +973,10 @@
         "EffectBlock",
         "EventDecl",
         "FormatWrnOptions",
+        "IslandBuildResult",
+        "IslandDiagnostic",
+        "IslandInput",
+        "IslandStrategy",
         "LexError",
         "Lexer",
         "LoadBlock",
@@ -999,7 +1003,9 @@
         "analyzeOptimizations",
         "analyzeRuntimeImports",
         "analyzeRuntimeRequirements",
+        "assertReactAvailable",
         "assertValidAst",
+        "buildIslands",
         "compilationKey",
         "compile",
         "compileNativeWrnFile",
@@ -1015,19 +1021,26 @@
         "generate",
         "generateBrowserModule",
         "generateDeclarations",
+        "generateIslandEntry",
         "generateNative",
         "generateServerFunctionsModule",
         "generateStoreBrowserModule",
         "generateStoreModule",
         "generateTargets",
         "inferredRuntimeType",
+        "islandNamesFrom",
+        "islandPropValue",
         "optimizeAst",
         "parse",
+        "parseIslandStrategy",
+        "renderIslandMarker",
         "resolveWrnImport",
         "resolveWrnImports",
+        "routeNeedsIslands",
         "rpcManifest",
         "runtimeCapabilities",
-        "runtimeTypeOf"
+        "runtimeTypeOf",
+        "serializeIslandProps"
       ]
     },
     "@wrnexus/content": {
@@ -2279,6 +2292,16 @@
         "useWrnActions",
         "useWrnStore"
       ],
+      "./browser": [
+        "MountOptions",
+        "islandRootCount",
+        "mountIslands",
+        "remountIslands",
+        "setStoreResolver",
+        "unmountIslands",
+        "useWrnActions",
+        "useWrnStore"
+      ],
       "./runtime": [
         "getIslandRuntime"
       ]