Move the SDK demo to sdk-target-based-on-call-view-model

The `sdk/` directory is about to become the MatrixRTC SDK package, so the
demo that lives there — one bundle of Element Call's CallViewModel for a plain
page or widget — moves aside, unchanged. It keeps building under a script and
vite config of its own, `pnpm build:sdk-target-based-on-call-view-model`, into
its own `dist` rather than the repository root's, and no longer copies the
developer's config.json out of `public`. Its README says which script to run
and where the output lands.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

vite-sdk-target-based-on-call-view-model.config.ts

@@ -0,0 +1,32 @@
+/*
+Copyright 2025 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { defineConfig } from "vite";
+import nodePolyfills from "vite-plugin-node-stdlib-browser";
+
+// Config for the SDK demo that predates the sdk/ package: a single bundle of
+// Element Call's CallViewModel for a plain web page or widget. Kept building
+// until the harness in sdk/dev replaces it (see sdk-plan.md).
+export default defineConfig(() => ({
+  worker: { format: "es" as const },
+  // Relative URLs, so the bundle can be hosted under any path
+  base: "./",
+  // Otherwise the developer's own config.json in `public` is copied into the output
+  publicDir: false,
+  build: {
+    outDir: "sdk-target-based-on-call-view-model/dist",
+    sourcemap: true,
+    manifest: true,
+    lib: {
+      formats: ["es" as const],
+      entry: "./sdk-target-based-on-call-view-model/main.ts",
+      name: "MatrixrtcSdk",
+      fileName: "matrixrtc-sdk",
+    },
+  },
+  plugins: [nodePolyfills()],
+}));