feat(android): 增加独立Android原生离线工程与GitHub Actions自动化构建

- 原生工程物理隔离：新建 android/ 独立工程，零侵入 Web 端现有源码
- 自动化资产同步：通过 android/copy-web-assets.sh 在构建时复制 Web 静态资产
- 原生体验调优：沉浸式状态栏适配、明文HTTP与DOM存储支持、返回键防误退
- 高清图标生成：基于 icon-512.png 自动生成全套 mipmap 分辨率桌面图标
- 云端CI构建：添加 .github/workflows/build-apk.yml 支持一键/Tag打包输出 APK

android/app/src/main/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools">
+
+    <uses-permission android:name="android.permission.INTERNET" />
+    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
+    <uses-permission android:name="android.permission.VIBRATE" />
+
+    <application
+        android:allowBackup="true"
+        android:icon="@mipmap/ic_launcher"
+        android:roundIcon="@mipmap/ic_launcher_round"
+        android:label="@string/app_name"
+        android:supportsRtl="true"
+        android:theme="@style/Theme.WorkHours"
+        android:usesCleartextTraffic="true"
+        tools:targetApi="31">
+
+        <activity
+            android:name=".MainActivity"
+            android:exported="true"
+            android:configChanges="orientation|screenSize|keyboardHidden"
+            android:windowSoftInputMode="adjustResize">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
+    </application>
+</manifest>

android/app/src/main/java/top/ouaone/workhours/MainActivity.java

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+package top.ouaone.workhours;
+
+import android.annotation.SuppressLint;
+import android.content.Intent;
+import android.graphics.Color;
+import android.net.Uri;
+import android.os.Build;
+import android.os.Bundle;
+import android.view.View;
+import android.webkit.ConsoleMessage;
+import android.webkit.WebChromeClient;
+import android.webkit.WebResourceRequest;
+import android.webkit.WebSettings;
+import android.webkit.WebView;
+import android.webkit.WebViewClient;
+import android.widget.Toast;
+
+import androidx.activity.OnBackPressedCallback;
+import androidx.appcompat.app.AppCompatActivity;
+
+public class MainActivity extends AppCompatActivity {
+
+    private WebView webView;
+    private long lastBackPressTime = 0;
+    private static final long BACK_PRESS_INTERVAL = 2000; // 2秒双击防误退
+
+    @SuppressLint("SetJavaScriptEnabled")
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+
+        // 设置状态栏与导航栏外观
+        setupSystemBars();
+
+        webView = new WebView(this);
+        webView.setBackgroundColor(Color.parseColor("#1E293B"));
+        setContentView(webView);
+
+        configureWebSettings();
+        setupClients();
+        setupBackNavigation();
+
+        // 加载打包在 assets 中的离线应用
+        webView.loadUrl("file:///android_asset/www/index.html");
+    }
+
+    private void setupSystemBars() {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
+            getWindow().setStatusBarColor(Color.parseColor("#1E293B"));
+            getWindow().setNavigationBarColor(Color.parseColor("#F8FAFC"));
+        }
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+            View decor = getWindow().getDecorView();
+            int flags = decor.getSystemUiVisibility();
+            flags |= View.SYSTEM_UI_FLAG_LIGHT_NAVIGATION_BAR; // 浅色导航栏图标
+            decor.setSystemUiVisibility(flags);
+        }
+    }
+
+    @SuppressLint("SetJavaScriptEnabled")
+    private void configureWebSettings() {
+        WebSettings s = webView.getSettings();
+        s.setJavaScriptEnabled(true);
+        s.setDomStorageEnabled(true);
+        s.setDatabaseEnabled(true);
+        s.setAllowFileAccess(true);
+        s.setAllowContentAccess(true);
+        s.setAllowFileAccessFromFileURLs(true);
+        s.setAllowUniversalAccessFromFileURLs(true);
+        s.setMixedContentMode(WebSettings.MIXED_CONTENT_ALWAYS_ALLOW);
+        s.setUseWideViewPort(true);
+        s.setLoadWithOverviewMode(true);
+        s.setSupportZoom(false);
+        s.setDisplayZoomControls(false);
+        s.setCacheMode(WebSettings.LOAD_DEFAULT);
+    }
+
+    private void setupClients() {
+        webView.setWebViewClient(new WebViewClient() {
+            @Override
+            public boolean shouldOverrideUrlLoading(WebView view, WebResourceRequest request) {
+                Uri uri = request.getUrl();
+                String scheme = uri.getScheme();
+                if ("http".equalsIgnoreCase(scheme) || "https".equalsIgnoreCase(scheme)) {
+                    // 仅当点击外部链接且不是同步 API 时调用系统浏览器
+                    String url = uri.toString();
+                    if (!url.contains("/api/")) {
+                        try {
+                            Intent intent = new Intent(Intent.ACTION_VIEW, uri);
+                            startActivity(intent);
+                            return true;
+                        } catch (Exception ignored) {
+                        }
+                    }
+                }
+                return false;
+            }
+        });
+
+        webView.setWebChromeClient(new WebChromeClient() {
+            @Override
+            public boolean onConsoleMessage(ConsoleMessage cm) {
+                // 控制台日志过滤输出到 Logcat
+                android.util.Log.d("WorkHoursWebView", cm.message() + " -- From line "
+                        + cm.lineNumber() + " of " + cm.sourceId());
+                return true;
+            }
+        });
+    }
+
+    private void setupBackNavigation() {
+        getOnBackPressedDispatcher().addCallback(this, new OnBackPressedCallback(true) {
+            @Override
+            public void handleOnBackPressed() {
+                long now = System.currentTimeMillis();
+                if (now - lastBackPressTime < BACK_PRESS_INTERVAL) {
+                    finish();
+                } else {
+                    lastBackPressTime = now;
+                    Toast.makeText(MainActivity.this, "再按一次退出工时记账", Toast.LENGTH_SHORT).show();
+                }
+            }
+        });
+    }
+
+    @Override
+    protected void onResume() {
+        super.onResume();
+        if (webView != null) {
+            webView.onResume();
+        }
+    }
+
+    @Override
+    protected void onPause() {
+        if (webView != null) {
+            webView.onPause();
+        }
+        super.onPause();
+    }
+
+    @Override
+    protected void onDestroy() {
+        if (webView != null) {
+            webView.destroy();
+        }
+        super.onDestroy();
+    }
+}

android/app/src/main/res/values/colors.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <color name="primary">#4F46E5</color>
+    <color name="status_bar_color">#1E293B</color>
+    <color name="nav_bar_color">#F8FAFC</color>
+    <color name="window_background">#1E293B</color>
+</resources>

android/app/src/main/res/values/strings.xml

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+<resources>
+    <string name="app_name">工时记账</string>
+</resources>

android/app/src/main/res/values/styles.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <style name="Theme.WorkHours" parent="Theme.AppCompat.DayNight.NoActionBar">
+        <item name="android:statusBarColor">@color/status_bar_color</item>
+        <item name="android:navigationBarColor">@color/nav_bar_color</item>
+        <item name="android:windowBackground">@color/window_background</item>
+        <item name="android:windowLightStatusBar">false</item>
+        <item name="android:windowLightNavigationBar">true</item>
+    </style>
+</resources>