Migrate data paths to ~/.local/share/fluorine/, add native build, fix %command% and system Proton scanning

- All data paths migrated from ~/.var/app/com.fluorine.manager/ to
  ~/.local/share/fluorine/ so native and Flatpak builds share the same
  instances, plugins, and configs
- New fluorinepaths.h/.cpp with fluorineDataDir() helper and one-time
  migration from old path (writes MOVED.txt breadcrumb)
- New libs/nak/src/paths.rs as Rust equivalent (data_dir())
- Strip %command% tokens from launch wrapper in protonlauncher.cpp
- Always scan /usr/share/steam/compatibilitytools.d/ for system Proton
  packages (Arch installs Proton there); add Flatpak filesystem permission
- Native build (build-native.sh) installs to ~/.local/share/fluorine/
  with desktop entry and ~/.local/bin symlink instead of portable zip
- build-flatpak.sh wrapper for Flatpak builds
- Fix container locale (LANG=C.UTF-8) for AutoUic warnings
- Fix prefixExists() to handle both compatdata and pfx directory layouts
- Fix globalInstancesRootPath() to use fluorineDataDir() on Linux
- Fix umu-run Flatpak lookup to use fluorineDataDir()
- Update README with build instructions and Arch dependency list

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/libs/nak/src/paths.rs b/libs/nak/src/paths.rs
new file mode 100644
index 0000000..4b212b9
--- /dev/null
+++ b/libs/nak/src/paths.rs
@@ -0,0 +1,12 @@
+//! Shared data directory for Fluorine Manager.
+//!
+//! All data lives under `~/.local/share/fluorine/` — accessible from both
+//! native and Flatpak builds (the Flatpak has `--filesystem=home`).
+
+use std::path::PathBuf;
+
+/// Returns the Fluorine data directory (`~/.local/share/fluorine`).
+pub fn data_dir() -> PathBuf {
+    let home = std::env::var("HOME").unwrap_or_else(|_| "/tmp".to_string());
+    PathBuf::from(home).join(".local/share/fluorine")
+}