chore: checkpoint web Blender feature-gap work, docs and tests

- update native web_engine sources and rebuilt wasm artifacts
- add task cards, status notes and tooling scripts
- add web e2e specs, tutorial UI sources and tutorial assets
- sync golden task manifests and audit records

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

tools/web/qa/opfs-sync-worker.js

@@ -0,0 +1,76 @@
+/* QA-only Dedicated Worker: exercises OPFS createSyncAccessHandle modes. */
+const handles = new Map();
+
+function reply(requestId, payload) {
+  self.postMessage({ requestId, ...payload });
+}
+
+async function resolveFile(path) {
+  const segments = String(path).split("/").filter(Boolean);
+  if (!segments.length) throw new Error("empty OPFS path");
+  let directory = await navigator.storage.getDirectory();
+  for (const segment of segments.slice(0, -1)) {
+    directory = await directory.getDirectoryHandle(segment, { create: true });
+  }
+  return directory.getFileHandle(segments[segments.length - 1], { create: true });
+}
+
+self.onmessage = async (event) => {
+  const data = event.data ?? {};
+  const requestId = data.requestId ?? "";
+  try {
+    if (data.op === "capability") {
+      reply(requestId, {
+        ok: true,
+        hasSyncMethod: typeof FileSystemFileHandle !== "undefined" &&
+          typeof FileSystemFileHandle.prototype.createSyncAccessHandle === "function",
+        isDedicatedWorker: typeof DedicatedWorkerGlobalScope !== "undefined",
+      });
+      return;
+    }
+    if (data.op === "acquire") {
+      const file = await resolveFile(data.path);
+      const mode = data.mode ?? "readwrite";
+      let handle;
+      try {
+        handle = await file.createSyncAccessHandle({ mode });
+      }
+      catch (error) {
+        if (mode === "readwrite-unsafe" && error instanceof TypeError) {
+          reply(requestId, { ok: false, unsupportedMode: true, mode, name: error.name, message: error.message });
+          return;
+        }
+        throw error;
+      }
+      handles.set(data.id ?? requestId, handle);
+      let written = 0;
+      if (data.write !== undefined) {
+        written = handle.write(new Uint8Array(data.write), { at: 0 });
+        handle.flush();
+      }
+      reply(requestId, { ok: true, mode, size: handle.getSize(), written });
+      return;
+    }
+    if (data.op === "close") {
+      const handle = handles.get(data.id ?? requestId);
+      if (handle) { handle.close(); handles.delete(data.id ?? requestId); }
+      reply(requestId, { ok: true, closed: Boolean(handle) });
+      return;
+    }
+    if (data.op === "close-all") {
+      for (const handle of handles.values()) handle.close();
+      handles.clear();
+      reply(requestId, { ok: true });
+      return;
+    }
+    reply(requestId, { ok: false, name: "QA_OPERATION_INVALID", message: String(data.op) });
+  }
+  catch (error) {
+    reply(requestId, {
+      ok: false,
+      name: error?.name ?? "Error",
+      message: error?.message ?? String(error),
+      stack: String(error?.stack ?? "").slice(0, 1200),
+    });
+  }
+};