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>

knip.ts

@@ -12,7 +12,7 @@ export default {
     config: [
       "vite.config.ts",
       "vite-embedded.config.ts",
-      "vite-sdk.config.ts",
+      "vite-sdk-target-based-on-call-view-model.config.ts",
       "vite-component.config.ts",
       "vite-component-dev.config.ts",
     ],