feat: add android manifest, strings (DE+EN), colors, base theme

READ_CALENDAR permission declared. Strings split into English master
(values/) and German (values-de/) with the Loading/Failure/Success
generic state strings used across screens. Backup rules let DataStore
back up by default with no file-based content. Theme stub delegates
real theming to Compose; the Activity-level XML theme only sets
transparent system bars and dark-mode hint.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/src/main/AndroidManifest.xml

@@ -0,0 +1,30 @@
+<?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.READ_CALENDAR" />
+
+    <application
+        android:name=".CalendulaApp"
+        android:allowBackup="true"
+        android:dataExtractionRules="@xml/data_extraction_rules"
+        android:fullBackupContent="@xml/backup_rules"
+        android:icon="@mipmap/ic_launcher"
+        android:label="@string/app_name"
+        android:roundIcon="@mipmap/ic_launcher_round"
+        android:supportsRtl="true"
+        android:theme="@style/Theme.Calendula"
+        tools:targetApi="35">
+        <activity
+            android:name=".MainActivity"
+            android:exported="true"
+            android:label="@string/app_name"
+            android:theme="@style/Theme.Calendula">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
+    </application>
+
+</manifest>