fix: Add dark mode support for adaptive icon background

Fix launcher icon visibility issue in dark mode where white background
made the white logo invisible.

Changes:
- Add values-night/ic_launcher_background.xml with dark color (#111214)
- Dark background ensures white logo remains visible in night mode
- Matches the app's night theme color scheme (night_default_page_bg)
- Light mode continues to use light background (#EEEEEE)

Before: White icon on white background (invisible in dark mode)
After: White icon on dark background (visible in dark mode)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: graycreate

app/src/main/res/values-night/ic_launcher_background.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <!-- Dark background for adaptive icon in night mode to ensure white logo is visible -->
+    <color name="ic_launcher_background">#111214</color>
+</resources>