Add app source for F-Droid release (v1.0.6)

Adds the full Android source tree, Gradle wrapper, fastlane store
metadata and the fdroiddata build recipe so F-Droid can build from
source. README gains build instructions and an updated structure tree.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015g6ECVSKcBG8CJPrqC3G5o

build.gradle.kts

@@ -0,0 +1,6 @@
+plugins {
+    id("com.android.application") version "9.2.1" apply false
+    // Not applied to modules: only pins the Kotlin version used by AGP's built-in Kotlin
+    id("org.jetbrains.kotlin.android") version "2.4.0" apply false
+    id("org.jetbrains.kotlin.plugin.compose") version "2.4.0" apply false
+}