Epub reader themes (#97)

* Implemented a custom theme engine for the EPUB reader, allowing users to switch between built-in themes (System, Light, Dark, Sepia, Slate, and OLED).

Key changes include:
- Added `ReaderThemePanel` and theme selection logic to `EpubReaderScreen`.
- Introduced a theme persistence layer using SharedPreferences.
- Updated `ChapterWebView` and `epub_reader.js` to dynamically apply background and text colors via JavaScript, including improved contrast adjustment for inline styles.
- Enhanced `CssParser` and `ContentStyler` in the paginated reader to adapt CSS colors based on the active theme's background and text luminance.
- Integrated theme-specific background and text colors into `PaginatedReaderScreen` and its layout components.
- Added a theme palette icon to the reader controls.

* Added custom theme builder and texture support to EPUB reader

* Refactored color picker(PDF) into shared components and enhanced EPUB theme editor

* Updated theme customization UI and improved WebView theme application efficiency

* Updated page flip animation to use paper color with a theme-based tint

* Improved state restoration during paginated reader reconfiguration

app/src/main/res/drawable-nodpi/palette.xml

@@ -0,0 +1,10 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="960"
+    android:viewportHeight="960"
+    android:tint="?attr/colorControlNormal">
+  <path
+      android:fillColor="@android:color/white"
+      android:pathData="M480,880Q398,880 325,848.5Q252,817 197.5,762.5Q143,708 111.5,635Q80,562 80,480Q80,397 112.5,324Q145,251 200.5,197Q256,143 330,111.5Q404,80 488,80Q568,80 639,107.5Q710,135 763.5,183.5Q817,232 848.5,298.5Q880,365 880,442Q880,557 810,618.5Q740,680 640,680L566,680Q557,680 553.5,685Q550,690 550,696Q550,708 565,730.5Q580,753 580,782Q580,832 552.5,856Q525,880 480,880ZM480,480Q480,480 480,480Q480,480 480,480Q480,480 480,480Q480,480 480,480Q480,480 480,480Q480,480 480,480Q480,480 480,480Q480,480 480,480L480,480Q480,480 480,480Q480,480 480,480Q480,480 480,480Q480,480 480,480Q480,480 480,480Q480,480 480,480ZM303,503Q320,486 320,460Q320,434 303,417Q286,400 260,400Q234,400 217,417Q200,434 200,460Q200,486 217,503Q234,520 260,520Q286,520 303,503ZM423,343Q440,326 440,300Q440,274 423,257Q406,240 380,240Q354,240 337,257Q320,274 320,300Q320,326 337,343Q354,360 380,360Q406,360 423,343ZM623,343Q640,326 640,300Q640,274 623,257Q606,240 580,240Q554,240 537,257Q520,274 520,300Q520,326 537,343Q554,360 580,360Q606,360 623,343ZM743,503Q760,486 760,460Q760,434 743,417Q726,400 700,400Q674,400 657,417Q640,434 640,460Q640,486 657,503Q674,520 700,520Q726,520 743,503ZM480,800Q489,800 494.5,795Q500,790 500,782Q500,768 485,749Q470,730 470,692Q470,650 499,625Q528,600 570,600L640,600Q706,600 753,561.5Q800,523 800,442Q800,321 707.5,240.5Q615,160 488,160Q352,160 256,253Q160,346 160,480Q160,613 253.5,706.5Q347,800 480,800Z"/>
+</vector>