Add breastfeeding duration tracking and UI improvements

Features:
- Breastfeeding timer: Click to start, stop to save duration
- Manual duration input: Long-press for NumberPicker (1-60 min)
- Edit breastfeeding duration: Click on duration in event details
- Day separators: Visual dividers between days in event list
- German translations: Added missing strings for puke/bath events,
  time units, amount labels, signature settings, event details

The breastfeeding timer state persists across app restarts.

app/src/main/res/layout/breastfeeding_timer_dialog.xml

@@ -0,0 +1,35 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:layout_gravity="center"
+    android:gravity="center"
+    android:orientation="vertical"
+    android:padding="20dp">
+
+    <TextView
+        android:id="@+id/breastfeeding_side_emoji"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:textSize="60sp"/>
+
+    <TextView
+        android:id="@+id/breastfeeding_timer_display"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginTop="20dp"
+        android:textSize="48sp"
+        android:textColor="@color/accent"
+        android:fontFamily="monospace"
+        android:text="00:00"/>
+
+    <TextView
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginTop="10dp"
+        android:textSize="14sp"
+        android:textColor="@color/grey"
+        android:text="@string/breastfeeding_timer_hint"/>
+
+</LinearLayout>