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, 2 insertions, 7 deletions

diff --git a/libs/nak/src/steam/proton.rs b/libs/nak/src/steam/proton.rs
index 064fd96..4059dc4 100644
--- a/libs/nak/src/steam/proton.rs
+++ b/libs/nak/src/steam/proton.rs
@@ -56,8 +56,6 @@ pub fn find_steam_protons() -> Vec<SteamProton> {
         return protons;
     };
 
-    let is_flatpak = steam_path.to_string_lossy().contains(".var/app/com.valvesoftware.Steam");
-
     // 1. Steam's built-in Protons (steamapps/common/Proton*)
     protons.extend(find_builtin_protons(&steam_path));
 
@@ -65,11 +63,8 @@ pub fn find_steam_protons() -> Vec<SteamProton> {
     protons.extend(find_custom_protons(&steam_path));
 
     // 3. System-level Protons in /usr/share/steam/compatibilitytools.d/
-    if is_flatpak {
-        crate::logging::log_info("Flatpak Steam detected - skipping system protons in /usr/share/steam/compatibilitytools.d/");
-    } else {
-        protons.extend(find_system_protons());
-    }
+    //    (Arch packages Proton here; Flatpak has --filesystem=/usr/share/steam:ro)
+    protons.extend(find_system_protons());
 
     // Filter to only include Proton 10+ (required for Steam-native integration)
     protons.retain(is_proton_10_or_newer);