Dark mode

Compose's MyApplicationTheme already had a DarkColorScheme defined and
defaults to isSystemInDarkTheme(), but the activity-level XML theme was
hardcoded to android:Theme.Material.Light.NoActionBar — so cold-start
window background and the splash screen flashed bright cream regardless
of the system setting, then snapped to dark when Compose drew its first
frame.

- values/themes.xml: parameterise windowBackground via a color resource
  rather than the hardcoded Light theme default.
- values/colors.xml: add window_background = #FFFBF0 (the cream we use
  in light mode).
- values-night/themes.xml: dark-variant of Theme.MyApplication parented
  on android:Theme.Material.NoActionBar.
- values-night/colors.xml: window_background and splash_background both
  switch to #14110A — same deep warm-black as the Compose dark scheme
  background, so the splash → app handoff is seamless.

Verified on the emulator with `cmd uimode night yes`: list, formatted
view, and the WYSIWYG editor all switch cleanly to dark, with all
formatting (heading sizes, inline B/I/U/S, tables, images, link colors,
checkbox states) still legible and on-brand.

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

Author: ericmigi

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

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <!-- Splash backdrop in dark mode — match the deep warm background of the
+         Compose dark color scheme so the splash → app handoff is seamless. -->
+    <color name="splash_background">#14110A</color>
+    <color name="window_background">#14110A</color>
+</resources>

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

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+
+    <!-- Splash inherits the same Theme.SplashScreen parent; the night-mode
+         color resources (windowSplashScreenBackground, window_background,
+         etc.) are picked up automatically via the values-night/colors.xml
+         overrides — no separate splash style needed. -->
+
+    <style name="Theme.MyApplication" parent="android:Theme.Material.NoActionBar">
+        <item name="android:windowBackground">@color/window_background</item>
+    </style>
+</resources>

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

@@ -2,4 +2,7 @@
 <resources>
     <!-- Cream background that matches the launcher icon's notepad. -->
     <color name="splash_background">#FFF8E5</color>
+    <!-- Activity window background — also used as the cold-start backdrop
+         before Compose paints. values-night overrides for dark mode. -->
+    <color name="window_background">#FFFBF0</color>
 </resources>

app/src/main/res/values/themes.xml

@@ -8,5 +8,7 @@
         <item name="postSplashScreenTheme">@style/Theme.MyApplication</item>
     </style>
 
-    <style name="Theme.MyApplication" parent="android:Theme.Material.Light.NoActionBar" />
+    <style name="Theme.MyApplication" parent="android:Theme.Material.Light.NoActionBar">
+        <item name="android:windowBackground">@color/window_background</item>
+    </style>
 </resources>