build(rechner): exact expression engine, keypad, scientific panel, history, memory; README

Co-Authored-By: Claude Opus 5.5 <[email protected]>

rechner/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">
+    <!-- no INTERNET: a calculator has nothing to send anywhere -->
+    <uses-permission android:name="android.permission.VIBRATE" />
+    <application
+        android:allowBackup="true"
+        android:icon="@mipmap/ic_launcher"
+        android:roundIcon="@mipmap/ic_launcher"
+        android:label="@string/app_name"
+        android:supportsRtl="true"
+        android:theme="@android:style/Theme.Material.NoActionBar">
+        <activity android:name=".MainActivity" android:exported="true" android:windowSoftInputMode="stateAlwaysHidden">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+                <category android:name="android.intent.category.APP_CALCULATOR" />
+            </intent-filter>
+        </activity>
+    </application>
+</manifest>