fix(data): route data_dir() through a per-platform shim so Android persists

dirs::data_dir() returns None on Android, which silently disabled
every persistence path (settings, stats, achievements, replays,
game-state, time-attack sessions, user themes). New
solitaire_data::platform::data_dir() shim falls through to
dirs::data_dir() on desktop and returns the per-app sandbox at
/data/data/com.solitairequest.app/files on Android — no JNI needed,
since the package id is pinned in
[package.metadata.android].

CLAUDE.md §10 already flagged this as a known pitfall; the shim
pays it down at the one chokepoint instead of per feature.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

solitaire_data/src/achievements.rs

@@ -15,7 +15,7 @@ const FILE_NAME: &str = "achievements.json";
 
 /// Platform-specific default path for `achievements.json`.
 pub fn achievements_file_path() -> Option<PathBuf> {
-    dirs::data_dir().map(|d| d.join(APP_DIR_NAME).join(FILE_NAME))
+    crate::data_dir().map(|d| d.join(APP_DIR_NAME).join(FILE_NAME))
 }
 
 /// Load achievements from an explicit path. Returns `Vec::new()` if the file