feat: add basic tauri client app

client-app/src/preload/Readme.md

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+# Preload Scripts
+
+Here are preload scripts (See [tauri's doc](https://tauri.app/v1/references/architecture/inter-process-communication/isolation)). This is simillar to Electron's [preload script](https://www.electronjs.org/docs/latest/tutorial/sandbox#preload-scripts).
+
+We pass env variables to AFFiNE side from here.

client-app/src/preload/index.ts

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+/* eslint-disable @typescript-eslint/ban-ts-comment */
+
+// tauri preload script can't have `export {}`
+// @ts-ignore 'index.ts' cannot be compiled under '--isolatedModules' because it is considered a global script file. Add an import, export, or an empty 'export {}' statement to make it a module.ts(1208)
+window.__TAURI_ISOLATION_HOOK__ = payload => {
+  console.log('Tauri isolation hook', payload);
+
+  return payload;
+};
+
+/**
+ * Give AFFiNE app code some env to know it is inside a tauri app.
+ */
+function setEnvironmentVariables() {
+  window.CLIENT_APP = true;
+}
+
+setEnvironmentVariables();