docs: Comprehensive README update with new features and architecture details

- Add extensive documentation for offline mode, sync, collections, and dashboard features
- Document new Material You theming, OLED mode, and widget capabilities
- Include detailed sections on metadata extraction, Markdown editor, and import/export
- Update technology stack versions (Kotlin 2.0.0, Hilt 2.51.1, Retrofit 2.11.0, Room 2.6.1)
- Simplify installation and compilation instructions
- Add user guide with first-time setup and

build.gradle.kts

@@ -4,4 +4,5 @@ plugins {
     alias(libs.plugins.jetbrains.kotlin.android) apply false
     alias(libs.plugins.hilt) apply false
     alias(libs.plugins.ksp) apply false
+    alias(libs.plugins.kotlin.serialization) apply false
 }