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/java/com/aryan/reader/paginatedreader/PaginatedReaderViewModel.kt

@@ -72,6 +72,8 @@ class PaginatedReaderViewModel : ViewModel() {
         textStyle: TextStyle,
         density: Density,
         isDarkTheme: Boolean,
+        themeBackgroundColor: androidx.compose.ui.graphics.Color,
+        themeTextColor: androidx.compose.ui.graphics.Color,
         context: Context,
         initialChapterToPaginate: Int?,
         mathMLRenderer: MathMLRenderer
@@ -83,7 +85,7 @@ class PaginatedReaderViewModel : ViewModel() {
 
             // CSS Parsing and Font Loading
             val userAgentStylesheet = UserAgentStylesheet.default
-            var allRules = OptimizedCssRules() // CHANGED from: mutableListOf<CssRule>()
+            var allRules = OptimizedCssRules()
             val allFontFaces = mutableListOf<FontFaceInfo>()
 
             val uaResult = CssParser.parse(
@@ -92,9 +94,11 @@ class PaginatedReaderViewModel : ViewModel() {
                 baseFontSizeSp = textStyle.fontSize.value,
                 density = density.density,
                 constraints = textConstraints,
-                isDarkTheme = isDarkTheme
+                isDarkTheme = isDarkTheme,
+                themeBackgroundColor = themeBackgroundColor,
+                themeTextColor = themeTextColor
             )
-            allRules = allRules.merge(uaResult.rules) // CHANGED
+            allRules = allRules.merge(uaResult.rules)
             allFontFaces.addAll(uaResult.fontFaces)
 
             book.css.forEach { (path, content) ->
@@ -104,9 +108,11 @@ class PaginatedReaderViewModel : ViewModel() {
                     baseFontSizeSp = textStyle.fontSize.value,
                     density = density.density,
                     constraints = textConstraints,
-                    isDarkTheme = isDarkTheme
+                    isDarkTheme = isDarkTheme,
+                    themeBackgroundColor = themeBackgroundColor,
+                    themeTextColor = themeTextColor
                 )
-                allRules = allRules.merge(bookCssResult.rules) // CHANGED
+                allRules = allRules.merge(bookCssResult.rules)
                 allFontFaces.addAll(bookCssResult.fontFaces)
             }
             val fontFamilyMap = loadFontFamilies(
@@ -125,6 +131,8 @@ class PaginatedReaderViewModel : ViewModel() {
                 density = density,
                 fontFamilyMap = fontFamilyMap,
                 isDarkTheme = isDarkTheme,
+                themeBackgroundColor = themeBackgroundColor,
+                themeTextColor = themeTextColor,
                 bookId = bookId,
                 bookCacheDao = bookCacheDao,
                 proto = proto,