Refactor: Introduce EdgeToEdgeHelper for consistent inset handling

This commit introduces an `EdgeToEdgeHelper` class to centralize and simplify the application of window insets for edge-to-edge display.

Key changes:
- Created `EdgeToEdgeHelper` to manage padding based on system bar insets.
- Migrated various Fragments (`OverviewFragment`, `OnboardingFragment`, `SettingsFragment`, `TroubleShooterFragment`) to use `EdgeToEdgeHelper` for consistent padding.
- Removed manual inset handling from `Activity2` and `Fragment2` as `EdgeToEdgeHelper` now manages this.
- Enabled edge-to-edge display in `MainActivity`.
- Minor updates to `BillingClientConnection` for product details fetching and `build.gradle.kts` for configuration.

app-common/src/main/java/eu/darken/capod/common/uix/Activity2.kt

@@ -3,7 +3,6 @@ package eu.darken.capod.common.uix
 import android.content.Intent
 import android.os.Bundle
 import androidx.appcompat.app.AppCompatActivity
-import androidx.core.view.WindowCompat
 import androidx.lifecycle.LiveData
 import eu.darken.capod.common.debug.logging.Logging.Priority.VERBOSE
 import eu.darken.capod.common.debug.logging.log
@@ -16,8 +15,6 @@ abstract class Activity2 : AppCompatActivity() {
     override fun onCreate(savedInstanceState: Bundle?) {
         log(tag, VERBOSE) { "onCreate(savedInstanceState=$savedInstanceState)" }
         super.onCreate(savedInstanceState)
-
-        WindowCompat.setDecorFitsSystemWindows( window, false )
     }
 
     override fun onResume() {

app-common/src/main/java/eu/darken/capod/common/uix/Fragment2.kt

@@ -7,8 +7,6 @@ import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
 import androidx.annotation.LayoutRes
-import androidx.core.view.ViewCompat
-import androidx.core.view.WindowInsetsCompat
 import androidx.fragment.app.Fragment
 import eu.darken.capod.common.debug.logging.Logging.Priority.VERBOSE
 import eu.darken.capod.common.debug.logging.log
@@ -42,17 +40,6 @@ abstract class Fragment2(@LayoutRes val layoutRes: Int?) : Fragment(layoutRes ?:
     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
         log(tag, VERBOSE) { "onViewCreated(view=$view, savedInstanceState=$savedInstanceState)" }
         super.onViewCreated(view, savedInstanceState)
-
-        ViewCompat.setOnApplyWindowInsetsListener(view) { v, insets ->
-            val systemWindowInsets = insets.getInsets(WindowInsetsCompat.Type.systemBars())
-            v.setPadding(
-                v.paddingLeft,
-                systemWindowInsets.top,
-                v.paddingRight,
-                0
-            )
-            insets
-        }
     }
 
     override fun onActivityCreated(savedInstanceState: Bundle?) {