feat: add Android target and default TreeNodeRow to tree-structure-compose (#39) (#48)

Add the `android` target to the Compose Multiplatform library and a sensible
default renderer, so the largest Compose audience is a first-class consumer.

- Core `tree-structure` and `tree-structure-compose` now build and publish an
  `-android` variant (compileSdk 35, minSdk 21). The core needs it too: its
  inline `tree { }` DSL is built per target, and Android consumers (JVM 11/17)
  cannot inline a JVM-21 build.
- `TreeNodeRow`: a foundation-only default node row (clickable, indented, with a
  `▾`/`▸` marker, no Material dependency), plus a no-content `LazyTree(root,
  label = …)` overload that uses it. The existing lambda overload is unchanged.
- New `samples` Android app module demonstrating `LazyTree` + `@Preview`
  (not published; excluded from API validation).
- Toolchain: Gradle wrapper 8.5 -> 8.10.2, Android Gradle Plugin 8.7.2.
- binary-compatibility-validator now emits per-target dumps (api/jvm, api/android)
  for the two multi-JVM-target modules; CI assembles the Android outputs.

CHANGELOG.md

@@ -6,6 +6,19 @@ All notable changes to this project are documented here. The format is based on
 
 ## [Unreleased]
 
+### Added
+- **Android target.** The core `tree-structure` module and `tree-structure-compose` now publish an
+  `-android` variant (`minSdk` 21), so both can be consumed directly in Android projects.
+- `tree-structure-compose`: a foundation-only `TreeNodeRow` composable — a sensible default node row
+  (clickable, indented, with a `▾`/`▸` marker and no Material dependency) — plus a no-content
+  `LazyTree(root, label = …)` overload that renders each node with it. The existing lambda overload
+  is unchanged.
+- A runnable Android sample app in the new `samples` module, with `@Preview` composables.
+
+### Changed
+- Upgraded the Gradle wrapper to 8.10.2 and introduced Android Gradle Plugin 8.7.2 (`compileSdk` 35).
+  No source or behavior changes to existing targets.
+
 ## [4.1.1] - 2026-06-08
 
 ### Fixed